I used a hair dryer and WD40. Takes some time, be patient, but they will come off. I had a bad experience with Goof Off on the rear cowl, took my paint off, but the tank is metal so maybe you would not have a problem on the tank. Hair dryer really softens up the tank stickers good. Then start peeling slowly. I happened to have long fingernails at the time so I peeled a mm off at a tiime. If you do a search it has been discussed a good bit previously.
Yup just removed mine then about 15 mins for the complete job heat gun and a credit card once they are off wd 40 removes the left over glue and Ipolished it and waxed it not a mark to be seen but do take you time mate be patient Grasshopper