When you buy a new garage door, you can either set it up yourself or let a professional contractor do it. The latter option might be best in these cases.
The Existing Door Has Ample Damage
If the reason why you're installing a new garage door on your property is that the existing door is severely damaged, then you should probably hire a contractor for new garage door installation. After all, the existing door might be pretty difficult to move and detach from your property.