Unscrew the nut until it is flush with the top of the shaft. Spray with PB Blaster, pull up on the shaft and tap on the nut. It has to be flush so you don't mushroom the threads. A puller is handy. I use a harmonic balancer puller when threaded holes are available in the steering wheel on each side of the shaft. If the puller can't be used, you may have to let the PB soak a day or two. Re-reading your post, if it is a bolt, unscrew it just enough to see a little clearance under the head of the bolt. Pull up on the wheel and tap on the bolt, but not too hard. I pulled one on a Toyota pickup one time and had the nut completely off. Was hitting the underside of the wheel near the center with my hands. The wheel came off too easy. Busted my lip.