Removing vinyl graphics in order to update them will vary in difficulty depending both on surface and age. Newer graphics on glass may be easily peeled off, whereas graphics that have spent years being weathered onto the side of a van will be harder work.
Experts seem to agree that the three essential ingredients to removing vinyls without damage are heat, pulling and patience.
Heat: Your goal is to melt the adhesive glue, without damaging the surface the vinyl is adhered to. A hairdryer on a medium setting could attain the desired result – ensure you have a corner of the vinyl lifted first, ready to pull.
Pulling: Using fingers at the edges of the graphic to pull is the best way to achieve removal, and the recommended technique is to keep your fingers very close to the surface (wall, glass, etc) while pulling, to avoid the graphic coming apart. Work your fingers constantly down the graphic as you pull, keeping within millimetres of the surface.
Patience: Go slowly! Graphics, especially old ones, will fall apart without much encouragement, so going slowly is more likely to keep it one sheet and remove cleanly. So find and edge, heat the graphic, then pull slowly while keeping your fingers close to the surface.
Once you have a graphic off you may need to remove any remaining glue left behind. For this you may need a product, or some alcohol, to aid with dissolving and wiping away the adhesive. Be sure to use something non-damaging to the surface you’re working with.
There are tools that can help with the graphic removal part of this task, although if working with painted/sprayed surfaces such as vans you need to remember the potential for scraping off paint as well as graphics! Likewise, glass has a coating on it, which can be damaged if you don’t use the right tools. Either be sure you are confident, or ask an expert.