then you already know what OCing is, it can be dangerous to your hardware without taking the right precautions, and via the motherboard BIOS settings.
to elaborate, which in this case is likely the CPU; OCing raises the CPU clock speed for all cores beyond what is normally shown (certain boost functions like intel's turbo boost raises the clock speed while turning off a core at a time. i.e; i5-4670K = 3.4ghz w/ 4 cores > 3.8 w/ 1 core). this raises performance in some but not all applications.
in turn, the CPU may generate more heat, which will shorten the CPU lifespan. more true if you also raise the voltage to achieve a higher OC. this is why it's highly recommended to get a third party heatsink like CM's Hyper 212 EVO to cool the CPU and mitigate the damage. getting a good motherboard with a good power phase design may also help to get a stable OC.
performing an OC takes patience. usually done via the BIOS/UEFI settings, preferably with an unlocked CPU (i5-3570k/4670k, i7-3770K/4770K, FX-4300/6300/8300, etc.) and an accompanying overclockable board (in intel's case, usually the Z*7/Z*5 chipsets only. AMD's more lenient). you got 2 components to OC; the multiplier and the Bclk. the latter's rarely recommended as it can cause stability issues. the former is only possible with an unlocked CPU. normally, you raise the multiplier a bit, and maybe lower the Bclk, to raise your clock rate (multi x Bclk = clock speed, so 34 x 100mhz = 3400mhz = 3.4ghz, for example. you can raise it to 40 x 100mhz to get 4.0ghz). you then run a stress test to ensure it's stable. if it is, you can raise it further, and repeat the test till you reach a point where it's unstable. from there, you can lower the clock back to the last stable setting, or raise the voltage a tiny bit (hence also raising the heat generated) to achieve stability and/or a higher OC. you will eventually hit a wall where you can't OC and raise the voltage any more, not without shifting to a custom liquid cooling solution. how high you can OC without doing so is dependent on how good a chip you got, i.e. your luck.
read a proper guide like the one thatvietguy posted for a better explanation and a more comprehensive walkthough.