Enter the 'Lineup' menu and select a player to sell. Put him into the reserves by
pressing B and selecting the 'Move To Reserves' option. Then, press R to enter
the 'Comparisons' screen. Select the player you want to put into reserves, then
press B and choose a player you want to buy. Then, press X to swap. When the
swapping screen appears with the clock, try to get there football to go past the 0 in
the middle. When they do so, move your football on top of theirs. You will now
swap players and they will have to pay you.