To access any locked level, input this sequence while viewing the Map: (LRDXRLUY).
Clear Save Data
To clear all save data: press and hold LB, RB, Left Thumbstick and Right Thumbstick while viewing the Map.
Play in Easy Mode
On the Title screen, using the Left Thumbstick, X and Y buttons, enter: (XDUYLRXY). If you entered it correctly you will hear the "objective clear" tune. Now press START and proceed to play the game.