hey I am not a 100% sure but I think u should go to your bios adn have there clock speed and there you are suppossed to have the multipliers and play with it.For instance if your proccessor is 2.0 ghz you are suppossed to have the multipliers 20 x 10 or something like that,but make sure you have a really good heatsink and cpu cooler otherwise it's gonna overheat and then bye bye proccs. hope that i am helping you at least a bit.If your mobo is old then you have jumpers,but I don't think you have to deal with that anymore.it should be through your bios.
good luck