When car window stickers have been fixed to a windscreen for a long period of time they sometimes can be difficult to remove. Over a prolonged period the adhesive on the car window stickers will become very aggressive. However by following the process outlined below all car window stickers should be capable of being removed leaving no adhesive residue.
Firstly lightly run a solvent based product such as alcohol, or lighter fuel to the car window stickers until it gets absorbed. Take a sharp blade, preferably a razor blade, and press firmly against the glass. Move the blade under the corners of car window stickers and slowly work inwards. This will pick up the vinyl part of the car window stickers and the also should start lifting the adhesive. This should be enough to remove the car window stickers but there may still be an adhesive residue left behind. If this is the case just repeat the process by applying more solvent and leave for a few minutes. Again use blade to the scrape off the excess adhesive. Continue to do this until all of the adhesive has been removed. Finally wash the area with a detergent based product such as washing up liquid to remove any traces of solvent. You will now have a clean area to apply your new car window stickers.