Normal size players
Pause the game, then hold L1 + Triangle and press the following combination:
Right(2), Up, Down(2), Left, Right, Left.
Mini-players
Pause the game, then hold L1 + Triangle and press the following combination:
Up, Left, Down(2), Right, Down, Up, Left.
All Apparel and Footwear
Hold L1 + Triangle and press the following combination at the Main menu:
Right(2), Left, Up(3), Down, Left.