Load or reset the game, then execute the following BASIC command before running or restarting the program.

Code - Effect

POKE 4217,X SYS 319 - Set number of lives (X represents the desired number of lives)
POKE 4469,76 POKE 4470,124 POKE 4471,17 SYS 319 - Unlimited lives
POKE 5571,197 - Unlimited lives