If they aren't making noise (like grinding/scraping/growling noises), and the wheel will spin relatively smooth, without being "notchy" or "grabby", then they are likely just loose and need to be taken apart, cleaned, repacked and reinstalled. If you are not familiar with repacking bearings, do an internet search for how to do it. You don't just goop some grease on the outside of them and call it good....you have to either use a bearing packing tool, or your hand, and work the grease into the inside of the bearings.
You should do both the inner and outer wheel bearings.
Figure an all day job, since you haven't done them before.
There are 2 seals that go on the backside of the wheel hub (you can't see them until you pull the wheel hub off). I think most places call them inner and outer wheel hub seals (it refers to where they are on the backside of the hub). One seal will have to be removed in order to remove the inner wheel bearing (there is also a snap ring under the seal that has to come off, that actually holds the bearing in). The Federal Mogul part numbers for the seals are 710240 and 710239.
