1998 Opel Corsa Over heating

Hello, my car has a terrible heating problem, and i've been told by the mechanic that the cylinder head needs to be repaired.I also have another problen where the engine is very noisy, like the tappets are a problem and I find changing to the fifth gear is a major problem.I dont want to offend any mechanics but many a time they lied to me about the repairs on my car thus it always cost me a fortune and now i'm afraid to be taken for a ride again, can you teach me to fix my own car, like a step by step on how to repair my car.I am a technician and it wont be a problem to learn.