The following cheats require you to start Mission 1: Silvan. Head to the first room with the two baddies in it. Kill 'em and enter the room. Input the following codes inside....
Press L1 + L2 + R1 + R2 + X. A blue light will confirm.
Press L1 + L2 + R1 + R2 + triangle. A green light will confirm. Press start and exit the level. At the main menu you can change the level with the D-pad.
It's easy to put in if you do it fast! Just push Triangle, Square, Up, Down, Down during the game.
Thanks to Revolution readers Captain Canada, Jayme Green, Simon Price, bowdown, and Micheal Yeom!