Since I only used "managed" solutions I don't need to concern myself with such. Had you tried the WHM's manual though at their site? I am assuming it should inform you the commands you need to know about their software?
Follow the steps to update and verify license
- Login to your server as root
- Run the below command
/usr/local/cpanel/cpkeyclt
- Once its updated successfully, Try login cPanel/WHM panel
- Verify cPanel license with server IP