Swapping a garage door opener yourself is doable if the door and track are in good shape - it's bolting a unit to the ceiling and wiring a safety sensor pair, and plenty of people do it. Where it stops being a weekend project is exactly where Sawyer's housing stock tends to put you: a door old enough that the track, hinges, or spring are original, because then you're not installing an opener, you're diagnosing a system you can't fully see until you're inside it.
We won't talk anyone out of trying the straightforward case. What we will say is that a torsion spring under tension is not a place to improvise, and if your garage was built around 1963 and nothing's been touched since, assume the spring is original until someone confirms otherwise. That's the one call where paying for a look before you buy a DIY opener kit saves money rather than costing it.