There are adhesive removers that will do it easily and won't harm the paint. Rapic-Tac makes a great one. Be careful with the heat gun also. Better to use it at more of a distance, not right on top of the letter so you heat up more area of the metal. You can burn the paint or make the metal expand too much and crack the paint. Wear gloves too.
I added the black GMC letters to be installed on my truck at delivery and the dealership did a crap job so there's a lot of micro scratches on the paint in the middle of the letters, any recommendations for how to polish that?
I am going to use this method to remove the chrome lettering of my Colorado pickup, then replace with blacked out letters, matte finish. I think my ride will look MUCH BETTER afterwards 😎👍