How to disable overclocking?

My computer MSI CX61 2PC-499US I ordered at XOTIC PC and got it overclocked professionally. It works perfectly but I wan't to have a way to disable it so I can play minecraft without any white flicking. I have been told to goto the bios and I know how to get there but I don't know what to do when I get there. I have windows 8.1 if that helps at all

Go to the BIOS, look on the last page for something like "Load Optimum Defaults" or similar. Click that item and then "Save Changes".

I did load optimization Defualts. It ended up not helping it still flickers white a lot