cut a slot in the bit of bolt sticking up , dremmel with cutting disc is best but a junior hacksaw with a fine tooth blade will do ,make sure the slot is nice and neat, get a flat blade screw diver to fit the slot , needs to fit nice n snug so shape the screwdriver with a file or the dremmel to fit , spray the bolt with WD40 and let it soak for a bit push down hard on the driver to stop it slipping and damaging the slot , turn left!!