HexCheat:

 Here is a possibility to choose all levels directly from beginning.
 Save the game in slot one and load the file save1.dat into the
 hex editor. Now search hex position 101.
 There should be a 01 with means that you are in level 1 at the
 moment. If you edit this position with 01-09, 0A-0F and 11-14 you
 are able to choose the level you want to play. The game has 20
 levels, the highest value is 14.