1999 Ford Taurus rear hub and bearing assembly

Drive Train Axles Bearings problem
1999 Ford Taurus 6 cyl Front Wheel Drive Automatic

I am trying to replace the rear bearing hub assy on my 99 ford tauris the instrusct instruct me to take the nut off of the rear bearing stud . I don't know how to get the metal nut retaing off and what to do about replacing it. How do I get the nut off and what size socket do i need

thanks