Did you ever buy a used car from someone and then wonder how to get that, "My kid is an honor student..." bumper sticker off the rear bumper? I have found that a hair dryer will assist in removing almost any sticker from any surface. The trick is to heat the area slowly and thoroughly before attempting removal and without over heating the material you are removing the sticker from.
Start out by warming the entire area of the sticker and warm a little of the surrounding area also. Once the sticker is warm to the touch, then beginning at one corner, carefully focus the heat on that area while attempting to peel back the corner of the sticker. Work slowly by keeping light tension on the sticker while heating the area in front of where you are pulling. What you are doing is softening the adhesive which holds the sticker in place. The newer the sticker is, the better the process works but I have successfully removed very old stickers and I have even successfully removed mailing labels from old magazines using this method.
If any adhesive remains after your sticker is removed, there's a product called Goo Gone which works nicely on hard, colorfast surfaces. If you are unsure about how your newly sticker free surface will react to a cleaning agent, you may want to consider alternatives such as good hot water or even a little clean dish water. Alternatively, you may simply continue to heat the cleared area and remove as much adhesive as possible by blotting very lightly with a lint free cloth.