They are taper roller bearings and inner with oil seal and an outer. The outer shells are pressed into the drum and can be removed and refitted with a drift but I got the shells fitted at a trailer workshop.
The inner and outer bearings have a different number as one has an oil seal and the other doesn't. The number is stamped into the bearing so you should be able to identify it when you have removed it.
Chock the wheels, jack up and remove the wheel. Remove the dust cap then the split pin and castellated nut and washer. The break drum then comes off easily as long as the hand brake isn't on. The bearings come away with it.
Get the shells changed, pack the bearings with bearing grease and refit. The oil seal bearing goes on first. Tighten the castellated nut while rotating the drum. The nut should not be tight, finger tight or so only, and there should be no play. Tighten and loosen, tighten and loosen as you rotate the drum until it feels right. Then fit a new split pin, cap etc.
I removed both of mine and took them to Honeyfield trailers in Bristol who had the bearings in stock. They also fitted the shells for me.