Two methods I know of, having sheered many a bolt in my time.
If some of the bolt is above the hole, use a stud remover. Basically a large nut, with a hole through it and a cam which tightens on the stud as you turn it.
If the top of the bolt is flush with the hole, you need an easy out. With this method, you drill a hole into the remains of the bolt. you tap the whole with a reversed thread (tap will be in the kit) you then screw the provided stud into the hole and as you keep turning it, it pulls out the stud.
Other than that, there is the cheaper method of just drilling it out, re-tapping it and then using a slightly larger bolt.
