Well, since all the proper methods have already been listed again and again, I'll offer two alternatives just because they are available, but any of the above combos will work.
The film can be scoured as opposed to heated to aid in a soapy residue penetrating the glue from behind (like the type you use for wallpaper) and if you want something less volatile or maybe more handy than acetone or lighter fluid to remove the left over tacky stuff, than regular corn or vegetable oil will also work fine. Peanut butter works also believe it or not but is messy.