Best thing to do is check Youtube for a few videos on how to grease trailer bearings. It is really easy, but a bit messy. I like to use medical gloves, for easy cleanup.
There are two methods, The first is to use the Ezlube option. There was a post recently on the subject, and it showed a YouTube video. You do have to be careful not to add the grease to quickly, or you will blowout the rear seal.
The other option, is to remove the brake drum, then removed the rear seal. then remove the bearings. There are a number of good YouTube videos showing all the details. I clean the bearings with WD40 and elbow grease, with a few rags. Then to repack the bearings. I put the grease in the palm of my hands and work it into the bearings quite well. Then I wipe a bit a grease on the sets slip the rear bearing in. install the new seals (need a board and hammer). Slip the drum back onto the spindle. Pack the front bearing, slip it on, again wipe a little grease onto the seat first, thread on the locking nut, tight, then back it off 1/4 to 1/2 turn. spin the hub, to check for tightness. dAd the safety spring lock. Basically your done. Its not hard to do.
While you have it apart you should check the breaks too.
Parts required, a tube of grease, and new rear seals.