At the main menu type 'fifthdimension'. 
Then use the following codes while playing the game: 

Key  Effect
---------------------
F1 - Return to normal 
F2 - Enlarge paddle 
F3 - Single gun 
F4 - Double gun 
F5 - Missile gun 
F6 - Laser 
F7 - Clear level 
F8 - Suicide 
F9 - Protective beam