A modern opener kit comes with a decent manual, and if you're comfortable on a ladder and patient with wiring, a straightforward swap on a door that's already set up right is within reach for a handy homeowner. Where it goes wrong is the force and travel-limit setup - get that wrong and the door either doesn't seal against the weatherstrip or it reverses on an obstruction it shouldn't, which is a safety problem, not a cosmetic one. The other place people get stuck is the header bracket. On houses from the mid-90s the header is usually solid enough for a direct remount, but we've been into attics where someone's original install was marginal and a new, heavier unit needs blocking added before it goes up. If you're not sure what's behind that board, that's the moment to stop and call rather than guess.