92Mustang92

I have an 88 GT with a 306 carburetored. I had the car for literally 8 days and had to replaced the radiator and cooling fans because they didn't cool down the engine while idling, the starter went, and now the cylinder blew. I just wanted to know where I can find upgraded cylinder heads to add more horsepower to the car and what are the general steps to replace the cylinder heads? Thanks