Usually they are adhered to the wall with silicone caulk, then another bead of caulk is put on to fill the crack between the wall and the backside of the backsplash. Cut that bead with a utility knife then start working several putty knives down behind the granite. Work from the top and the side and keep prying it out. Depends on the bond to the wall whether it will come off easy or not. If not, it will take some of the wallboard with it. You could try pouring some acetone down onto the silicone if you can pry the granite out far enough to be doable.