Loosen the clamp that's at the bottom of your bars, then pull your bars off once its loose. It may take a little effort, but if your clamp is loose you won't break anything.
Once that's off, find a wrench that will fit the top nut that's threaded onto your fork, and spin that thing right off.
Then, start loosening the second one. I would advise that you keep the fork pushed up while you do this, so that the bottom components of the headset don't fall out, which happens occasionally. So keep it resting on something so the fork doesn't slide down.
Once this top nut is off, pull the fork out carefully, and make sure you remember which way to put the bearing cage back in.
All you have to do now is put some grease in the headset cups, put the two nuts back onto your fork, spin it some, then put your bars on.