on the single disk I got to where I just bought new disk with the bearings in them the disk was usually warn enough to warrant it,
if the disk gets to small the boot wears more and they are expensive to replace,
I have ground off many rivets of the hubs and replaced the bearing as well, re riveting them, If there the iron bearings replace them with the anti friction bearing, it may need a spacer as well, for the change over, Deere should be able to guide you,there are aftermarket places that sell parts as well, like Shoups,
if it a double disk unit I think there is a hub cap and then either a right or left hand nut you loosen and remove the disk and press out the bearing, as the disk wears there ware spacer washers to set the disks so they cut a V and not a W as they wear smaller the disk do not cut as deep