A lot of owners are comfortable swapping a remote battery or resetting a code themselves, and that's fine - nothing risky there. Where it stops being a weekend project is anything involving the opener's travel limits, the force settings, or the safety sensor wiring. Get those wrong and you end up with a door that doesn't stop when it should, which is a real hazard, not a minor inconvenience.
The honest answer is that a full opener swap is a two-person, better-with-tools job - mounting the rail, setting the travel, aligning the sensors so they actually trip before something gets in the way. If you've done it before and have the hardware, go for it. If this is a first attempt and the unit is original to a house built in the late 1990s like most of what's around Surrey, it's worth having someone who's set a hundred of these do the alignment at minimum.