I always feel sorry for people who try to DIY a job WITH THE WRONG TOOLS and making it much more difficult than it really should be.
First, buy an adjustable wrench (also called a Crescent wrench). Harbor Freight. Just make sure that the jaws open wide enough to properly grip that nut. If that won't get the nut off, the spindle threads and the nut threads are probably damaged. One or the other or both will have to be replaced.
If that wrench does not remove the nut, you will need "brute force". Fond out the size of the nut (it could be inches or metric). Buy the proper size socket. Buy a "hand impact" (I don't know if HF has a 1/2" drive one but you can get them on Amazon). Buy a DECENT 24 oz ball peen hammer (not a rubber mallet !) and go to town !
