A single-car steel door, done carefully, is within reach for someone comfortable with a drill and a level - if you're only swapping panels on existing, sound track and springs. What isn't a DIY job, full stop, is torsion spring work. A wound torsion spring holds enough stored force to break a wrist or worse, and it's the single most common ER-worthy garage door injury. If your 1975-era house still has its original spring, treat it as due for replacement by a professional, not a project.
We also won't pretend every install is quick. If the header needs reframing for a taller or heavier door than the opening was built for, that's carpentry work before it's ever a garage door job, and it adds a day most homeowners don't plan for.