If you have 4 bolts that hold a cover plate on in the center of the backing plate, those usually hold the axle in place. After you take the 4 bolts out, you have to get a slide hammer and pull the axle out.

If you don't have a 4 bolt retainer, you may indeed have an axle that has c clips on the inner part of the axle, and you have to take the cover plate off the rearend to get these out.

If you do not have a slide hammer, a quick and dirty way to get the axle out is put the brake drum back on the studs backwards. Put 3 lugs nuts on till they are even with the tip of the studs, and then grab the drum and slam it back against the lug nuts. This is a poor man's axle puller, and will work unless the axle is really stuck.

P.S. Here's a link with some info, if you know what type rearend you have.
http://www.autozone.com/az/cds/en_us...rInfoPages.htm