To change your current level in your saved game, do the following:
 
 Hex edit SAND.SAV
 
 Change both offsets 4 and 7 to the one of the following:
 
 01 through 09  Missions 1-9          (I'm explaining hex values
 0A through 0F  Missions 10-15         for those who don't know.)
 10 through 14  Missions 16-20