Level Codes (all weapons, ammo and 9 lives):
Level 1: 6D7FBC0F
Level 2: 6DFBBC0F
Level 3: 6C77BC0F
Level 4: 6CF3BC0F
Level 5: 6F6FBC0F

Cheat: First bring ammo type 1 to 18 shots, then jump into a lava lake and immediately press the HELP key. You will lose a life, but after respawning you can now press HELP to refill energy and ammo anytime! You also get all weapons, 9 lives and 99 of everything. "Protected Mode" is also temporarily active, making you invulnerable. Pressing HELP again repeats all of this!