If the caulking does not pull off, try cutting with a single edged razor blade or utility knife. Be very careful not to cut to deep if it is a fiberglass shower stall. If there is any residue left that you want to clean off try WD-40, a rag and elbow grease on a small area. You should be able to rub off silicone caulking this way. If this dosent cut it try goof-off or xylene, CAUTION This is a strong solvent USE ONLY IN A WELL VENTLATED PLACE, this will remove any latex or acrylic caulking. Make sure that you mask off the area around the caulking if the shower is tile so that you don't smear the caulking into the grout.