Overclocking can be turned DOWN, or the settings can be reset to default (no overclocking). There are a few different ways in order to do this.
Depending on your motherboard, there may be a built-in reset switch, OR you can get into the BIOS and make the adjustments, OR another way to reset to factory defaults is to take out the real-time clock battery (CR 2032 Lithium flat battery) and leave it out for 10 minutes, and then replace the battery. On your computer, this CR 2032 battery is located at the lower right corner of the motherboard just to the left of the 1 1/2" x 1 1/2" blue component with the large white ASUS logo.
Care must be exercised when doing any work inside the computer case - proper anti-static grounding is a must (safeguard against static discharges, especially in winter).
If you are totally new to all this, I suggest that you do not attempt this by yourself.