Press ~ after starting the game at the screen where the items are
described. Proceed for two more screens and press [backspace] at 
the screen with the magic lamp. This enables the cheat mode. Then,
press one of the following keys during gameplay to activate the 
cheat.

Result                             Key
------------------------------------------------
Level Select                     - 1A through 1M
Level Skip                       - [keypad +]
Five Apples                      - A
Five Gems                        - G
Toggle Invincibility             - H
Toggle Free Movement             - M
Toggle Objects in some levels    - U