Overclock Rspberry Pi with raspi-config

To overclock your Raspberry Pi, enter the command:
$ sudo raspi-config

In the steps, use <UP/DOWN> key to select options, <Tap> to switch between options, and various actions. And <Enter> to confirm.

- Select Overclock and press <Enter>

Be aware that overclocking may reduce the lifetime of your Raspberry Pi. If overclocking at a certain level causes system instability, try a more modest overclock. Hold down shift during boot to temporarily disable overclock. 
See http://elinux.org/RPi_Overclocking for more information.

- Press <Enter> to confirm.

- Reboot.