Step 0: take pictures of your existing maps (or scan them if you have a scanner) to prevent further degradation and allow copying.
Step 1: insert each map image in your drawing tool as the background to a new map.
Step 2: draw as much or as little new information as you need.
Step 3: print maps for use during gaming if you need hardcopy.

These four simple steps let you get use out of your new toy without having to learn everything at once.