I couldn't pull up a manual on your board because I'm currently at work. But on most boards from that chipset series the settings to control fan speed are labeled as "Smart FAN" or "CPU Fan Control" and would be located in the "Hardware Monitor" section. Make sure your fan has all three wires connected to the board, the 3rd wire is RPM sensor which will allow the motherboard to detect and control the fan speed, usually this wire is the yellow one on a 3-Pin connector.