Pretty much the only thing you will need to buy/borrow is a strong adhesive remover. I Chose this automotive 3m adhesive remover because 3m is a good product and is available at local auto stores. Also you will need a rag, micro fiber or whatever you desire I recommend the micro fiber. I used fish string cause that is what I am used to but something as easy as floss string can be used.
Using the string, get it behind the letter and begin a sawing action while applying pressure and it will work its way off.
Now you are left with the glue, which can and will be very stubborn to remove. I found that moistening it with the adhesive remover wrag in conjunction with using a fingernail gently, became effective for me. Take your time and be gentle
Then repeat all this fun stuff for all your letters and make sure all the glue is removed from the paint when finished. Then go over it with a coat of wax just to get back that protection that the adhesive had removed.
*note this is how I do it, not responsible for any reckless behavior