From the main game menu, go into Options, and then into Pad Config. When in the Pad Config. menu, press and hold R2 and press Right, Down, Right, Tri, X. If you did the trick correctly, you will hear a confirming sound. Go back to the main menu and you should find a new option, Cheats. Start a game, pause it, and select Cheats. You can now access God Mode, All Weapons, and other cheats.