All Weapons and Infinite Ammo:
     While playing, go to pause screen and press Square, Cicle, R1, L1.

All Levels:
     At  the main menu, press and hold Square + L1 + R1 and then press
Up, Down, Left, Right.

Infinite Heath:
     At the main menu, press and hold R1 and L1 and then press Square,
Triangle, Right, Left, Cirlce, Square, Square, Right.