You really cannot do anything. your computer simply is not capable of running WoW effectively because it is unable to handle the strain. You need better hardware.
They also are just…badly designed in terms o thermodynamics.
I would never recommend a mac for gaming, or for anything to be honest. They are overpriced, when they break it is an utter headache to repair them. You can build a PC for the same price and it would accomplish much more.