On the title screen, Enter "CHEAT" for the password and press fire. Now start the game and use the following keys:
'F1'--For speed increase
'F2'--For faster bullets
'F3'---For better weapon
'F4'------------Not sure
'F5'------------Not sure
'F6'------------Not sure
'F8'-----For extra lives
'F9'------For level skip
'1'-'7'----Weapon select