hair dryer and a cleaner with orange oil seems to work good, thats what the ppl at vinyl places use
if its on a window I would use a scraper and a solvent for excess goo lol
. Warm the decals with a heat lamp. Peel off. Clean off excess glue with a paint-safe solvent.
a hair dryer works - be very careful with a 'heat gun' as they put out a few hundred degrees...and will bubble the paint :D