A torsion spring is under enough stored tension to break a bone or worse if it lets go while you're working on it - that's true everywhere, not just Keystone, but it's worth saying plainly since we won't walk a homeowner through doing it themselves over the phone. What you can reasonably check yourself: the door's balance (does it stay roughly in place when lifted halfway and released), whether the rollers are visibly worn or cracked, and whether the opener's travel limits need a simple adjustment. On a house from 1978, we'd also have you check if the track is still the original gauge, since some older setups used a lighter track than current code calls for, and that's a repair that waits for a tech anyway. Past that, the spring, the cable, and the drum are not a weekend project.