To OC the system. First read your manual and become familiar with your bios settings.
Now enter the bios and first lower the ram to the next lower speed. You either select a speed or a divider. Now find the pci lock and engage it. This way you are not overclocking the pci bus when you raise the fsb setting. This will improve your chances of an OC. Note if you do not have a board with a pci lock, you OC will be pretty small since you will be OCing the pci bus as well. This leads to data corruption, etc.
Once that is done, up the fsb [front side bus] from stock of 200 to something like 215. Save settings and exit. Now run a stability app like prime95 for single core or prime2004 for dual cores. It must be prime stable or it is not a stable OC. If there are no errors after at least 15min, restart and again up the fsb to something like 225 or so. Repeat the stability test. Once you go above a fsb of 225 or so, you will need to lower the HT [hyper transport] multiplier from 5 to 4. The idea here is to keep the HT bus as close to 1000 as possible. Continue to up the fsb until you find where you get an error in prime2004. When you do get an error, you now have a choice; backoff to a known stable OC or if you are brave, up the vcore [cpu core voltage] Only up the vcore by the smallest amount the bios allows. Repeat the test. If it is still unstable, you can again up the vcore however not more than twice. Note to find out if it is the ram or cpu causing the error, again lower the ram speed and repeat. If the errors continue, it is the cpu OC causing the problem. If you do not get errors with the lower ram speed, up the vdimm [ram voltage] and return the ram to the previous setting and repeat the stability test.
Note watch your temps; when you up vcore, temps will start to climb.