First check to see which version you are running: this is shown in the upper-right corner of your WHM screen. Then, check for the latest version on http://layer2.cpanel.net; If the version you are running is older than the current version, select the cPanel category then the Upgrade to Latest Version button or you can run “/scripts/upcp –force” from an ssh connection. You can also configure your server to automatically update itself by selecting the Server Configuration category, then Update Config, then select the Automatic radio buttons for the updates you wish to perform.
There are some blocks from one version to another you may need to be aware of. This information can be found here: https://documentation.cpanel.net/display/ALD/Upgrade+Blockers