A new door is not a weekend bolt-together job, and we'll say that plainly. Torsion springs store enough force to break a finger or worse if you don't know how to wind them, and a door hung even slightly out of square will bind, slam, or walk off the track within a season. If your opening is original to a mid-1970s build, there's also a decent chance the jamb isn't plumb anymore, which an install crew needs to account for with shims and fasteners a DIY kit won't include.
Where a homeowner can reasonably do their own work is the small stuff - swapping a remote, replacing a photo-eye sensor, lubricating rollers and hinges. New door installation, including spring sizing and track alignment, is not in that category.