What steps should I take before upgrading MariaDB?
We strongly recommend that you back up all of your databases before you upgrade MariaDB. It is also recommended that you keep a full cPanel backup of all of your user accounts before the upgrade.
Below is a link to an article which contains a list of resources on backing up your databases before an upgrade:
You should also take the time to review the recommended steps as documented by MariaDB in their official documentation.
The WHM Interface has a tool to help install the latest version of MariaDB that is offered for your Operating System. More information on this tool can be found in the cPanel Documentation.