Below is a video I found on the Practical Caravan YouTube page about how to remove old stickers from your caravan or motorhome. As the video shows it pretty straight forward you need to apply heat to weaken the bond. However its recommend not to use boiling water, not only for your own safety but also for the benefit of your paintwork and bodywork. You can also use a hairdryer for the same effect.
Once the sticker its self is removed you can use methylated spirits to remove the remaining glue and dirt. Not a bad idea to give it a polish afterwards to provide some protection.