I replaced my originals after 7 years, I had to take them to a shop that had a 50 ton press to get the old ones out. I already had the snap rings out so all they had to do was press out the old ones and the new ones in. You have to press on the inner race to get them out so they will be shot after you get them out. They used a flat bar to push the new ones in until they where even with hub and one of the old bearings to push them the rest of the way so the inner race never had any pressure on it.
I used Dexter bearings for $140 each that I could have got the same China bearing from etrailer for $90. The shop only charged me $50 to change them.
Denny