This video shows an easy, quick method for installing garage door rollers which doesn't require bending the track or removing hinges. Instead, if your setup is the same as the common setup shown in this video, you can simply remove the lower track and pull 4 rollers out at once.

For the upper roller, you can remove the bracket and replace the roller. Some doors may have a brackethinge combination hardware at this point: for this, you can still simply remove the fasteners and replace the rollers on these styles, as well.

Use all the normal precautions when working around garage doors. Do NOT fiddle with the torsion spring, and do NOT fiddle with the lower bracket or any bracket that has a cable attached.

Good luck with your repair!