Swapping a single roller on an unloaded section of track, with the door down and the spring untouched, is within reach for a homeowner who's handy. It's a hex wrench and a bit of patience.
Where it stops being a DIY job is anywhere near the bottom brackets, which are under spring tension even with the door closed, or anywhere the track itself needs to come off the wall. Bent track under load has put people in the ER trying to force it back into shape with a door still hanging on it.
Our honest limit here: if your rollers are original steel from a door built before the 1970s and the track's grooved, that's not a five-minute fix even for us - it's a full teardown of that section, and we'll tell you that before we quote it rather than after.