Rub the old decals off with alcohol. Let air dry, then wash down with cold water and a clean cloth and let air dry. Then apply the new decals smoothely and rub them down once they are on with dry cloth.
You can make your own decals. You can not make your own vinyl decals. These are cut on a special machine. There are kits for making waterslide decals on your computer and printing on a regular printer.
You can use your computer and printer to either copy or place original artwork on Lazertran Waterslide Decals. These decals can be cured and are extremely durable.