The Raspberry Pi is a capable little microcomputer. An old Pi can be overclocked to better handle newer and more demanding applications.
By far the only manner to modify the settings at the Raspberry Pi, assuming you’re running Raspbian or a derivative, is to definitely boot the device after which use the Raspi-Config tool to make changes.
If you’re using any revision of the Raspberry Pi 1 or 2, the config tool has a built-in menu for overclocking it. If you’re using a Raspberry Pi 3, you cant’t see an overclocking menu access for two reasons: 1) overclocking isn’t presently formally supported at the Pi three, and 2) the Pi 3 layout is so appropriate that it’s already running extraordinarily close to maximum settings all the time anyway, so there isn’t an entire lot of utility in overclocking it within the first place.
If your device is already at the terminal, you’re right where you need to be. If your device boots to the desktop, press Ctrl+Alt+F1 to kill the desktop and switch to the terminal view. (You can return the desktop when you’re done by entering the startx command.)
At the terminal, type sudo raspi-config and press Enter. (If you’re already logged in as root, you can drop the sudo part.) This will launch the configuration tool with a simple interface. Select entry 8, “Overclock” to continue.
You will see a warning that overclocking may reduce the life of your Raspberry Pi (because overclocked devices run hotter, and heat is the enemy of all electronics). You’ll also see a useful note about holding down the Shift key during boot if your system is unstable, which will boot the system with the default settings so you can troubleshoot it, and a link to the very informative eLinux wiki page about Raspberry Pi overclock settings. Choose “OK”.
Finally, you’ll be able to select the overclock preset you wish to use.
There are two camps regarding how you should approach overclocking. Some people prefer to start by stepping up the overclocking from a lower setting to a higher setting, backing off if there is any system instability. While that’s a really great rule to live by if you’re overclocking gear with untested settings, it’s a tad on the tedious side when you’re using settings pre-approved by the hardware manufacturer.