I replaced one of ours after it was a little loose. (about 60,000 miles) The next year another one was a little loose so I replaced the rest of them.
I have a 20 ton press and used varies spacers to get the first one out. I ground the race from the first one a little on the outside and used it to replace all of the new bearings.
One of the bearings had to be pressed in a tad to get the snap ring out. Other than that it was pretty straight forward.
Capn' Don
Pull your trailer and new bearings down and we will put it in our shop. After I point and you work about three hours your trailer will have new bearings.