Having done this in the past when riding a different board to what I was "supposed" to be I found this was the best way to do it without fucking anything, so yeah...
Chuck some Acetone into an old spray bottle, set it so its spraying more of a mist than spray, spray onto a cloth and start rubbing it into the graphic.
YOU DONT SPRAY IT ONTO THE DECK, look we know its going to do the job quicker, but the problem is that it can also fuck the glues.
Once the graphics off, do what you want to it and coat it in salba sauce.
Or you can just cover the graphic with stickerz