You need to remove the rear kuckle from the control arms, which involves taking out all the hardware, and removing the hub nut from the stub of the drive axle shaft. Once the knuckle assembly is completely removed, the best way to change the bearing is to have it done at a shop with a press, to push the old one out and install the new one. I've heard of people using a swing press (a hammer for you neophytes) to do this job, but you could easily run into trouble that way I think. Better to take the whole knuckle to a local shop with a press and have them do it, then reverse the procedure to re-install.
hope this helps
Ed Nicholson
SCCoO