Press TAB then activate the following cheats by entering the corresponding codes:

CHEAT FUNCTION - CHEAT CODE
Level select with cursor keys - ocellaris1q
Extra life for player one - ocellaris1l
Extra life for player two - ocellaris2l
Extra health - ocellaris1h
Fireball shots - ocellaris1f
Laser shots - ocellaris1z
Napalm shots - ocellaris1n
Missile shots - ocellaris1m
One C-bomb shot - ocellaris1c
One shield - ocellaris1s

Note: Replace the 1 in each code with 2 to activate that cheat function for player two.