To raise the clock speed of a graphics processing unit, central processing unit, or memory module by raising the front side bus (FSB) or the multiplier.
The end clock speed is determined by using the following equation
Multiplier * FSB = mhz
Sometimes additional voltage is required to achieve higher speeds.
Overclocking almost always requires more cooling than "stock" parts provide. And generally shortens the life of a componant.
I overclocked my Athlon by unlocking the multiplier and upping the FSB. I had to add .5v to make it stable though.