Assuming they are adhesive "stickers" and not water-slide decals. I would use a hair dryer or naphtha. You can buy a little squeeze bottle of Ronsonol lighter fluid (naphtha) which is handy for this type of work. Flood the sticker and keep it wet while removing it. Place the sticker on some wax paper until you are ready to reuse it. Photo-mount spray works well for this.
Jon Williams
Grants Pass OR USA