If you can easily reach it, wait until after dark and carefully cut the limb it is on and seal it in a plastic trash bag. Another option is to carefully cut it down at night and toss it into a fire(in a safe place!). Probably the easiest and safest way would be to saturate it with Raid! or other wasp & hornet spray, concentrating at the entrance. Do this at night when they are inside and inactive. This last method is the one I would use.
Good luck!

I wonder how judijerpen made out with the assault on hornets. That can be a rather intense situation if not handled correctly.