Harbor Freight (and others) sells a set of plastic trim removal tools which have worked well for me. By sliding one under the corner to open up a gap, then slide another one in to pry the panel away from the door. If the old panels are brittle or rotted they may break easily, so go easy. New door panels are easy enough to make but the rear side panels are another story. I recently had to find a good used set for my 122.