This question is asked very often, the simple answer is that it depends what kind of motherboard you are using.
Proprietary Computer manufacturers such as Dell, HP, Compaq, Gateway, IBM and most manufacturers use Intel motherboards that have the necessary BIOS options locked. For those users there is always hope, you can try using software overclocking programs, they do not work as good but can give you a boost.
One of the best software overclocking programs is Clockgen
If you are using a custom built computer and do not know if your motherboard has the required options, please download CPU-Z
and post its output on this forum to enable us to help you.