To remove a fiberglass shower pan you will want to start by removing excess water in the drainpipe. Take a turkey baster and put it down in the drainpipe to siphon out the water. Use a knife and cut along the edge of the fiberglass panel where it meets the linoleum. Put a rag in the drainpipe to keep any sewer gas from coming up. Next you want to drill the rubber flange material that is around the drainpipe out so that you loosen it up and allow the fiberglass pan to come loose from the drainpipe. Don't drill down more than an inch and make sure that you drill all the way around the drainpipe. Also use a utility knife to cut away some of the rubber flange. Vacuum up the pieces of rubber flange and remove the rag from the drainpipe. If the pan liner is clamped in you will have to remove those clamps also. Use a flat bar to pry up the pan and a screwdriver to hold the drainpipe down. Once the pan is loose just lift it up and out and you are ready to go.