In the Advanced Tab. Under performance you see Settings, click that. Now again go to advanced, processor scheduling would be best as Programs for gaming, and memory usage would be best as Programs for gaming.
I also recommend for good gaming, change virtual memory from automatic swap to custom from 2000 megabytes to 4000 megabytes.
Some might not recommend this, but the first thing you must know, automatic swapping does cost much CPU time itself, having a set amount keeps it from changing all the time and it never has to reset it's usage space, which it often does with Windows. They say doing this can make it slower, which it can. However for most games there are times where it must where it uses heavy memory and times it uses very little memory. Giving it a lot of roaming room is a good thing for games specifically.