Most likely they are foam taped to the wall with some silicone for good measure. Chance are the wall is going to get damaged. To what degree will be determined by your experience and what was used to install it. Just make sure the client knows that they may need to mud and repaint the area.
If there is tape left on the wall, use a little heat and roll it off. Too much or too little heat and the paint is guaranteed to come with it.