1. Spritz the sticker and the area around it with a little WD-40. The WD combined with the heat will dissolve the adhesive along the edges of the sticker, making it easier to peel back.
2. Allow the WD to sit for a few moments, and then begin warming up the sticker and the immediate vicinity with a hairdryer. You don't need to get the area blistering hot, and remember, you are working with a painted surface. Overheating the area can cause the paint to soften, making it easier to scratch.
3. As the sticker warms up you'll feel the surface become more pliable. When it does, start at one corner and slowly and carefully peel up the edge.
4. As the sticker lifts, apply a little heat to the leading edge. If the sticker starts to melt, ease up the heat. If it tears at some point, don't panic—you can remove the remnants later.
5. Once the sticker has been removed, wash down any leftover adhesive with WD-40, then use a clean rag to wipe the residue away.
HTH