Disconnect the garage door opener and close the door fully
Clamp the door in place with locking pliers or clamps on the track
Unplug the opener if needed and release the trolley from the door
Open the door manually just enough to access the roller you want to replace
Remove the hinge bolts or brackets holding the roller in place
Slide the old roller out of the hinge or track slot
Insert the new roller stem into the hinge
Reinstall and tighten the hinge bolts or brackets
Repeat for each roller one at a time
Check that each roller sits properly in the track
Remove the clamps and slowly test the door by hand
Reconnect the opener and test the door operation
Lubricate the rollers and track lightly if needed