Decals are easy to remove, but you probably won't be able to re-attach.
Heat gun's work well, just be careful of over-heating the vehicle surface if it is plastic or fiberglass. You can also just peel with your fingernails.
The decal may leave glue behind, there are lots of glue removers available at your local hardware or autoparts store, or WD-40 will work if you have the time.
1977 Safari Land Yacht
2005 Toyota Tundra SR5
2010 Ford Flex Ecoboost