REAR wheel hub assembly

I have a 99 Alero and have been getting a roaring noise from the rear and was told it was my wheel bearings; any info on how to replace these myself? Had the front ones done and I am new to the area and I think I got hosed (he's the one who told me the rear ones may need to be replaced). Would like to see if this is something I can do myself. Also any recommendations on the parts?