I’m not sure removing them is the best idea. The sun may have affected exposed areas differently from those covered, so you may well see the spaces of the stickers, even when off.
Removing is easy, however. I’ve removed some HOV lane stickers from plastic bumpers of cars, by using a hand-held hair dryer and plastic scraper. I work the sticker with fingers, at the same time, but overall the heat melts the glue underneath. When I get the sticker off, there is a glue mess beneath, and I wasn’t very successful with that.
i’d be careful if using a solvent to remove glue residue, as I’d worry about The paint underneath.
i’d just leave the stickers on. Let the next owner remove them, or not.
a lesson for all of us is to not put stickers on in the first place.