The trick to removing graffiti is to do it as soon as possible. Most graffiti is done with paint, which is applied wet and solidifies as the paint solvents evaporate. The solubility of paint, therefore, is reduced the longer it has a chance to harden. If you remove the paint right away, you will have a good chance of succeeding.
If you need to patch a large area in a stucco wall, call a mason or stucco specialist. But if the damaged area is no more than a couple of square feet, this can easily be done by yourself. Here’s how.