get a heat gun...heat stickers and peel off...get some reducer/paint thinner and remove excess glue

wet sand all the plastics with 400 wet and dry...

fthe tank sticker is usually clearcoated over....you have to remove the sticker by hard sanding or grinding it off...be careful not to cut the tank....use a wire wheel or something....after the stickers gone you will have to apply a little bit of filler to fill in the "asshole"where the sticker was...prime it and sand it with 400 also...