Removing decal

First try peeling the decal of the vehicle. In most cases this will not remove it completely but it's a good place to start.

Secondly you can try to use a single sided razor blade to scrape  the sticker. However, there is a chance for paint damage and/or injury if you are not careful with this method.

A safer more effective method is to heat the adhesive backing and peel the sticker. You can rent a heat gun for this or even use a hair dryer. Be careful not to over heat the air and cause paint damage. The best way to do this is to keep the heat gun or dryer a few inches away from the vehicle on low heat.

If there is still residual adhesive, you can try using a solution of water and alcohol and soaking the area for 10 minutes. The best way to apply the solution is with a spray bottle. If all else fails, most auto parts stores sell a selection of commercial adhesive removers that are safe for vehicle paint.

Removing existing decals

1. Use a heat gun or hair dryer to heat up a small region of the decal. This will make the decal more pliable and reduce the adhesive bond.

2.Starting at a corner, lift the decal away from the bodywork.

3.Use both hands as you get to the wider sections of the decal.

4.The heated area will cool off after a few minutes, causing the adhesive bond to increase again. You will notice that the tension will increase and the decal will tend to tear easily.

5.Simply repeat Step 1 and continue

After the decal is removed there may be adhesive residue remaining. Use an adhesive remover to remove residue. We really like the citrus-based adhesive removers like GooGone because they are non-toxic, bio-degradable, and can be readily found at hardware, department, and grocery stores.

 I hope this could help you removing the decals in your cars.

Are the decals on a painted surface or on a plastic bumper?

Use a heat gun, something stronger than a hair dryer, to soften the glue on that back of the decal, carefully remove th decal.  For the remaining glue do not use a solvent, this will remove the paint finish.  I think that Goo Gone may work. Check in Home Depot for something without a solvent to remove the excess glue.

Finger nail polish remover....That's it. I know it may sound crazy, but it does work. Pour it on the decal or soak it using a cotton ball and it will come off with no problem.

use regular paint thinners to remove glue from decals (both factory installed, and the annoying dealer advertising). If it's the good old factory finish, it holds up to this fine.

If you have the time and energy, there is a solution that will give you a show car finish. All factory finishes have "orange peel" to a certain degree. It's so subtle nobody really notices.

try a heat gun