First off, be aware of the risks. Second, make sure your motherboard and power supply are up to the job (in your case, that the mobo has a decent number of quality 'phases' and that it fully supports 125W+ CPUs, and that the power supply is decent and has decent amps on the 12V rail).
On startup of your PC, when you get the motherboard splash screen, press the 'setup' key (one example is DEL, varies across different mobos) on your keyboard. You will now be in the motherboard's UEFI.
Your mobo may have an automatic overclocking system called something like 'Easy OC', 'OC Genie', etc. You may use this if you are afraid of manual configuration.
If doing it the manual way, scrounge around the options until you find an option to change the CPU's 'clock multiplier'. Raise this SLIGHTLY. Now save and exit. You may also SLIGHTLY raise the voltage.
After booting into your OS, you will need to run some benchmarks like Prime95, Intel Burn Test, etc. If your system crashes or comes up with errors, restart and decrease the CPU clock multiplier and possibly voltage.
If it succeeds, you can either stay on your current overclock, or try and push it even further by upping the clock multiplier/voltage. Rinse and repeat.