Arcade To get to the 'GAME ASSIGNMENTS' press F2 and navigate down the menu. You will want to change 'ENEMY RANK' for your preferred difficulty.

GameCube & PS2 Find the settings through Options > Game Settings. You will want to change 'ENEMY RANK' for your preferred difficulty.

XBOX & PlayStation The settings are shown as you enter Arcade mode. You will want to change 'Difficulty' for your preferred difficulty.