How to upgrade CloudLinux 6 to CloudLinux 7?

There is no direct upgrade path from CloudLinux 6 to CloudLinux 7, therefore the only way is to move accounts to a new server with CloudLinux 7 installed.

This is due to the fact that a large number of 3rd party components (such as control panels) are installed on a typical CloudLinux 7 server, which makes it impossible to gracefully upgrade the OS without breaking control panels. Besides, at its core, any RHEL6-based system is much different from RHEL7-based systems (or higher).