Glued vinyl shower sheets can be removed from concrete walls using a joint knife and a chemical wallpaper remover. Cut into the top corner of the vinyl sheet, then pry it away until you can get a grip on it. Use pliers if you have trouble. Then, apply the liquid or gel wallpaper remover to help dissolve the adhesive. Follow instructions on the label to give the product enough time to loosen the adhesive, then scrape it away with a putty knife.