Removal overview

The main "trick" to removing vinyl graphics is Patience!

Different vinyls remove easier than other, some vinyls get "cooked-on" by the sun.

The basic technique is to push a squeegee (or some flat tool) against the edge of the graphics to lift  corner. Once the corner is lifted then slowly peel the vinyl up. if you go too fast then either some glue will remain or the vinyl will break.
A good way to prevent Breaking is to heat up the vinyl. Sometimes just parking the vehicle with the graphics in the sun will heat up the graphics enough. Other times you will have to use something like a Hair Dryer or a Heat Gun (caution is required to not damage the vehicle surface). This "heating" will help the vinyl Stretch instead of Breaking.

If glue is left on the vehicle then you must use a rag soaked in "Prepsol" or equivalent to soften the glue. Then you can squeegee the glue off. This is a very messy & time consuming process but multiple applications will succeed. If Prepsol is not working too well then you may use Petrol but be aware that this is very strong and may damage the surface so test some on a safe area.

If all fails then there are a few other steps you can take:

Good Luck (this is a great job for the apprentice)