We pull the panel pins holding the old rollers, work top-down, and check the track alignment at each bracket as we go - on a house from this era, 60 years of settling means the track is rarely still perfectly plumb even if nobody's touched it. We replace rollers in full sets rather than mixing old steel with new nylon on the same track; uneven roller diameter is a common cause of the grinding noise homeowners call us about after a partial DIY fix.
With the climate here running cold and severe through the winter, we default to sealed nylon rollers for anything we touch, since they don't need the lubrication steel rollers do and they don't contract the same way in a cold garage. Full set replacement on a two-car door usually runs under an hour once we're on site, start to finish including a track check.