[jambo]

It's a standard thread, so anti-clockwise to undo, but is generally on either finger tight or very very tight.

Make sure the tab washer is bent out so that it is not holding the nut in place, and then the easiest way is to get an air gun on it if possible. If you've not got one of those, put the bike in a high gear and get someone to use the rear brake while you get a breaker bar on the front sprocket. If the rear wheel still moves you can put something like a piece of wood through the rear wheel above the swing arm to stop it turning but if you do this be very careful of marking the wheel or swing arm, make sure you protect the finishes and use something big enough to spread the load.

Jambo