To activate the Heavy Metal F.A.K.K.2 cheat codes, you must first enable the game's console. To do so, select the Video/Audio menu and enter the Advanced section. Locate the console setting on the right side of the screen; make sure the console box contains a checkmark. During gameplay, press the tilde (~) key to open the console. With the console open, type in any of these codes followed by the enter key to activate the respective cheat code.
Pressing up after successfully entering a code will bring up the code you just entered. If you edit this previous code accordingly you can more easily and quickly enter the next code.