4xdog - You're right - Good point. It may just be the logistics that bug me.
- Open door and block it to remove tension.
- Screw door to blocks so it can't move when rollers are removed.
- Remove, repair, replace lower rollers.
If I could buy new ones it could be done at the same time and the garage door wouldn't be open for an extended period. Now that I have a real floor, I actually care, but I can throw a tarp down to reduce rain damage.
I expect to discover that I need to replace the upper center hanging rollers too. That is a little more interesting as the door has to be closed so once I remove it I'll have to crawl out of the window. Awkward yes, but feasible.
(I removed the - not original to the shed - side door during rehab as someone compromised the structure by cutting in a door right through a critical beam.)
Or I could remove the old stuff and jerry rig these in there: (pic linked to HD)