Do you have a 3M product or real Diamond Shield? Look for the Diamond installation decal that is usually mounted below the passenger side mirror. If you don't have one, you have 3M film. 3M solvent to remove the adhesive is available at autopart stores.
If you really have Diamond Shield, heat works the best to remove the film. Most of the time, no adhesive residue to deal with.
You can contact either company for recommendations.
Roger & Mary
2014 Tiffin Phaeton 36GH
2012 Honda Fit toad