Hit [Tab] to pause the game, the enter one of these:

ocellaris1q : Change levels, up/down arrow to change level
ocellaris1l : Player 1 extra life
ocellaris1h : Extra health
ocellaris1f : Fireball shots
ocellaris1z : Laser shots
ocellaris1n : Napalm shots
ocellaris1m : Missle shots
ocellaris1s : One shield
ocellaris1c : One c-bomb shot
ocellaris2l : Player Two (same as above, replace 1 with a 2)