To update cPanel, you can either do it through SSH, which is as simple as logging into the machine via SSH as root and using these two commands:

/scripts/updatenow
/scripts/upcp

or, you can do it through WHM, by going to the cPanel menu, and choosing Update to Latest Version

That's all! You should also go into update preferences in WHM and ensure you are not on auto updates, as these tend to break things, I recommend doing manual updates to the RELEASE tree!