Press Start to the Pause Menu and then enter the code.Full power up cheat is cumulative. After you use one, it deducts from the total.

For example:
At the beginning (stage 1), you have only 1 full power up cheat.
At stage 3, if you never use it, you have 3 full power up cheats.
At stage 5, you have 5 full power up cheats, etc.