A new garage door isn't a weekend bolt-on project, especially on an older opening. The door panels themselves aren't the hard part - it's the track alignment, spring tensioning, and making sure the opener (if you're replacing that too) is rated for the door's actual weight. On a house built when Whitewright's housing stock mostly went up, the opening may be out of square just enough that a big-box door kit won't seat flush without adjustment, and torsion springs are not something to guess at - a spring under tension that lets go can break fingers or worse. If you're handy and want to swap a few rollers or re-grease a track, that's reasonable. A full door swap, with the header work an older opening sometimes needs, is not a first-timer job.