From the Main Menu, press the Square button to acsess the Options Menu. From There, choose the "Enter Cheat" selection. (Caps Sensitive) 'worm' = Eddie Skin / 'zenmaster' = Brodi Skin / 'bronco' = Luther Skin. These cheats are acsessible at each riders detail screen, under cheat characters. You can't use any cheat characters as themselves, just as a skin to the players that you get in the beginning.