You may have already had a go at drilling it out, if not to do it you will need a pedestal drill and vice as you need to be fairly accurate with the drilling, use a drill a size or two smaller than the bolt and run the drill through it, the aim is to get a hole drilled through a size that you can then run a tap through to remove the remnants of the bolt that is held in the thread of the nut. The other way is to drill the bolt as above, then using a hacksaw blade cut a slot through the length of the hole you have drilled, you need to cut deep enough so the cut is at the bottom of the thread in the nut, starting at the cut using a small screwdriver if cold chisel you are usually able to get the remnants of the bolte loose enough to remove, you can also put another cut opposite the first.
Whilst this does do some damage to your nut I have found in past experiences there was no effect on the integrity of the nuts capacity to do its job,
good luck.
Beech
