when the main menu screen appears, highlight the options menu and press X, X, Y, Y, Left analog x2, Right analog x2, L trigger x2 and R trigger x2

go into the options menu and ya should have a cheats menu above the other options, if not keep tappin the cheat in but watch out when tappin the left and right ananlog sticks since ya can nudge them which throws off the cheat

in the cheats menu, ya will get a level select, exp level increase and enemy intelligence level( if detect ya or not when sneakin into a base)