depends how much you want to spend and what your skill levels are.
The easiest thing to do is just de-coke everything with emery paper so it's all nice and clean and re-seat the valves.
You could match the inlet and exhaust manifold ports to their respective manifolds with too much risk of
f-ing things up if it's the first time you done anything like this.
After that there's porting, but it's quite a risky job for a first timer as it's easy to make performance and fuel use worse if you do it wrong.
