1) Click on "Settings" Menu --> Then click "Options"

2) Move the "CPU Usage Control" right to a desired amount of CPU to be used. (1)

3) Check the CPU usage in your Windows task Manager (2). 

Setting the slider to Max gives you more chances to get rewards, but it also consumes more electricity and overheats your CPU. Use Slider to max with cautious when you CPU has a proper cooling. Setting CPU at 30% to 50% is also a good option. You will get rewards and you computer will still be responsive.