Hold L2 at the skater select screen, and press these combinations.

Effect	Code
Max All Stats	Triangle, Square, X.
Max Money ($999,999,999)	Triangle, Circle, X.
Unlock All Cheats	X, Circle, Triangle.
Unlock All Game Modes	X, Triangle, Circle.
Unlock All Levels	Triangle, Square, Circle.
Unlock All Skaters	Triangle, Circle, Square.
Unlock All Tricks	X, Square, Triangle.