Roller replacement is one of the more contained jobs we do. The tech unclips or unscrews the roller from the hinge, slides the old one out of the track, and sets the new one in - repeated per roller, usually all ten on a double door if the others are close behind the one that failed. On a 1987-era door, the bottom rollers often show the worst wear since they carry the most load crossing into the vertical track.
We check the track alignment while we're in there, because a bent track will chew through a brand-new roller just as fast as it did the old one - replacing the roller without straightening the track is a repair that doesn't hold. We'll flag that separately if we see it rather than fold it into the roller quote.
One limitation worth knowing: if the rollers are failing because the door itself has sagged or the panels have started to separate at the seams, a roller swap won't fix that. At that point we'll say so rather than sell a part that won't solve the actual problem.