To do this, you must have the following:

-Homebrew
-Homebrew app: Savegame installer
-Homebrew app: Savegame extractor

-Animal Crossing: City Folk, obviously
-ACToolkit

Now first of all, you must create a file on ACCF.
After you've done that, go to the Homebrew channel, and choose the app Savgeame extractor.
Follow the intrsuctions (just push A on the GC controller, or Reset on the Wii) and it'll
save a copy of your ACCF files onto the root of your SD card which will be in a file
called WIISAVES. In that folder, there'll be a folder called RUUE which is your ACCF
files. In that folder, they'll be some files. You don't and absolutely SHOULD NOT delete
anything in that folder even though the only thing you'll need to edit is the file called
RVFOREST which is your town. Everything else is important, but you don't need to do
anything to those files.

Okay, so after those files are on your SD card, go to the ACToolkit and click the Tom Nook
picture. That should allow you to choose a file. Go to the RUUE file in the WIISAVES
folder and choose RVFOREST. That should open up a little box. The options at the top will
be:
-File (Open, Save, Exit)
-Residents (Resident 1, 2, 3, 4, Residents Name, Fill out... [Catalog, Music])
-Town (View Town Map, Gate style [Stone, Wood, Brick], Grass Style [Style 1, 2, 3], Edit
Acres, Edit Town, Edit House [House A, B, C, D], Edit Lost and Found, Edit Recycle Bin,
Nook's Store [Edit Items, Clear sold out flags, Nooks Cranny, Nook 'n' Go, Nookway,
Nookingtons])
-Help (Colors, About)

Bellow that, there's Wallet which lets you choose how much money you want in it. It can
only go up to 99999. ABD lets you choose how much money you want in your bank. It can go
up to 9999999999. Points lets you choose how much Nook points you have. It can go up to
65535. Town name lets you choose your town's name.  Town fund just shows you how much
you've donated to the town hall.

Pockets lets you choose what items are in your pockets. Emotions lets you choose your
*emotions. Drawers lets you choose what items are in there. **Appearance lets you choose
what you look like.

*One of the emotions is called "Close". It's pretty funny. It only lasts a
second, and it's what happens when something is looking in their pockets, typing
something, looking at a picture, etc.

**If you don't know what your person will end up looking like, find a faq or some pictures
to look at.

If you choose 'Residents', "Residents Name" will let you change the residents
name for whatever resident you're on (1, 2, 3, 4). "Fill out..." will allow you
to fill either your Catalog with all the items, or put all the songs in your music player.

'Town' is the option that actually lets you edit your town.

Choosing "Gate Style" will change your gate style. 'Stone' is castle (blue),
'Wood' is... woodish (green), and 'Brick' is palace (pink).

Choosing "Grass Style" will change the style of your grass. I'm actually not
sure what this does, it may just change the shapes on the grass.

Choosing "Edit House" will only let you change the residents houses, not the
neighbours.

Choosing "Edit Lost & Found" or "Edit Recycle Bin" will let you
choose what items are in them.

Choosing "Nook's Store" will let you choose what items he's selling, change what
shop he has (Ex. Nookingtons) or clearing out the sold out flags, which means he's back in
stock again if you bought something from him that day.

Choosing "Edit Acres" will show you a picture of what the map of your town looks
like (without and houses or buildings and such). On the right, there's a + button that
says "Acres". When you click the +, there'll be a few more options: Barrier,
Normal, Oceanfront, River, Transition.
I'm sure that you don't need to do anything with Barrier, but if you'd like to, go ahead.
Normal will let you choose what height your town is at (Options 0-5) [Light green is the
lower height, darker green is the higher height], choose where your ponds are (6-11), gate
(12-15), gate+pond (16-17), etc. 
Oceanfront is the land infront of the ocean or the beach.
River is the rivers. You can choose what direction they go in.
Transition is the ramps.

It doesn't really matter where you place anything. I mean, there will be a few *glitches
if you don't put something in the right place, but everything is okay.

*You will be able to see outside of the acre, like the sky. It's just treated like a wall
though, nothing'll go wrong. It just makes it obvious that your town is hacked.

Now, if you want to choose where objects are located, choose "Edit Town". When
that opens up, you'll get another map of your town, but there will be little squares in
places. The big squares with all the little squares inside of them are the acres. Every
acre is 16x16, which means they all have 256 squares in each of them. 

Anyway, there are three + buttons on the side:
-Terrain (Anything that'd usually be natural outside of a house/building)
-Items (Anything you can use, wear, fish, bugs, floors, walls, and *DLC/HDLC)
-Furniture (Usually items that you put in your house)

*DLC is Downloadable Content which is put into the game by Nintendo.
HDLC is Hacked Downloadable Content which is put into the game by people who have hacked
into the game. HDLC may be hacked, but it does absolutely nothing to mess up your game.

At the top of the page, the options are:
-File (Import, Export, Apply, Exit)
-Tasks (Remove Items, Remove Terrain, Remove Weeds, Revive Flowers, Replenish Fruit,
Restore Grass, Remove Grass)
-View (Show Acre Grid, Show Background, Show items and terrain, Show grass, Show item
names on grid)

For 'File', I'm not sure if "Import" and "Export" are neccesary. Once
you've done sutff and finished with your town, just choose "Apply".

I'm pretty sure everything for 'Tasks' is obvious, sooo yeah.

Everything for 'View' is checked on. You can turn them off, if you'd like. It's better if
you leave them on, though.

Bellow those options, there is other options that say, "Item Controls",
"Building Controls", and "Grass Controls".

For Item Controls, you can choose an item from the + lists on the side, and push 'Place'
(or sometimes it pushes Place for you) and click somewhere on the grid to where you want
the item, or whatever you've chosen to be. 'Check' lets you see what the item is, and if
you push Place after that, you'll be placing that item somewhere. 'Delete' is pretty
obvious... and Bury/Unbury is, too. Just click the item that you want buried/unburied.

For Building Controls, you can 'Check' a building (which is a little B with white dots
around it) to see what it is, and then, you can choose 'Move' to move that building
somewhere else. I would not reccomend placing a building on the water, or having half of
the building on an edge, and half off. When you choose 'Place', a little box will show up
having options of different buildings from different events in the game. (Ex. New Years
Sign) Delete is a bit dangerous. You shouldn't delete anything important, like Nook's,
Town Hall, etc. It'd be okay to delete a neighbour, but.. it's kind of mean, lol. Also
feel free to delete signs, or move them to where you want new neighbours to live, because
wherever a sign is located, a neighbour can move there.

For Grass Controls, 'Check' shows you what the Quality is in the box beside it and for
'Set', just type what type of quality of grass you want, and click where you want it. 255
is the highest quality, 0 is obviously the lowest.

After you've finished doing whatever you wanted to do with your town, click File, then
Apply. Then you're back in the little box. Then click File, then Save.

It is reccomended to save another copy of your original town first just incase you want to
go back to it, or if you screwed something up.

So when you're sure you're done, go back to the Homebrew channel, and go to the app
Savegame installer. Push A on the GC controller or Reset on the Wii, and the town you made
will be saved to your game. 

Then, go check it out. Go see if you like it.

If you want to edit your town again, choose the Savegame extractor again so you won't have
to experience stuff that already happened that day. Say, if you had mail, saved and quit,
and then decided to edit your town again, then installed it, you'd have the exact same
mail that you just looked at. So don't forget to extract your game again before editing
it.

That's all folks. :D