In the section "Performance" the first option is "Overclocking Assistant" - select it an you will have two options: "Automatic" and "Manual". If you select "Automatic" you will see more options regarding the CPU frequency, RAM settings and so on. The easy way for you (if you are new in overclocking) is to leave it on "Automatic" and only change the CPU frequency - you will see a few presets, starting from 3.8 GHz up to 4.5 GHz. I would suggest you to select a value lower than 4.2 GHz, because the motherboard automatically change the voltage of the CPU (at 4.2 it will give you a maximum voltage of up to about 1.38 V, which is pretty high but still OK). Just be sure to have proper cooling (the stock one will not do).