Select "Code" at the main menu, then activate the following cheats by entering the corresponding symbols in the slots. A confirmation sign will appear to confirm correct code entry:

CHEAT FUNCTION - CHEAT CODE
Double player's health - Enter Eye, Thunderbolt, Skull, Hand, Boot as a code.
Double the damage of the player - Enter Hand, Boot, Skull, Eye, Thunderbolt as a code.
Unlimited ammunition - Enter Thunderbolt, Hand, Eye, Boot, Skull as a code.