signwriter by trade so iv done loads of sticker application and removal, warm the stickers up with a hair dryer or paint stripping gun (dont sound scared about that, its a trade secret for speed) one the sticker is warm, peel it off slowly and it should take the glue with it, if not use petrol to remove it (some people use nail varnish remover but this can f*ck up the o-rings in chains etc and as pointed out earlier diesel works well too but it stinks and its hard to get the smell out your hands)
one the glue is removed if there is any colour variation, use some good old fasioned original t-cut (not the colour match stuff cos thats actually a polish), wait till its dry, then rub off and its back to new, if ya like u can polish it afterwards but its not necessary.