No, yum update does not update the cPanel software itself; it updates the operating system's packages and software dependencies required by cPanel. To update cPanel & WHM, you must use the Upgrade to Latest Version interface in WHM or run the `/usr/local/cpanel/scripts/upcp script.

What yum update does:
Updates the server's operating system packages to their latest supported versions.
Updates software dependencies that cPanel & WHM require to run.
How to update cPanel & WHM:
In WHM:
Navigate to Home » cPanel » Upgrade to Latest Version and click the "Click to Upgrade" button.
From the command line:
Run the script /usr/local/cpanel/scripts/upcp.