Back in the early days of Linux, the changes to the OS were so dramatic that even when updating withing the same distro, in-place point release updates were problematic enough and it was always recommended that a major version release be done from scratch. There were just too many major changes to the underlying subsystems and package naming conventions. Doing an in-place update was just asking for trouble.
Modern distros have matured quite a bit although there are occasionally some major subsystem changes being made. Yet it's never been easier to do an in-pace major version upgrade.
I just did the upgrade on several Mageia3 systems and the results were consistent and satisfactory, not to mention simple.
Always backup critical information. Have a Mageia3 recovery disc on hand.
Reboot. You'll be using a new kernel, new glibc and so on.
$ sudo shutdown -r now
Run the package update command again. It should return with no packages needing updating.
Done. But . . . .
Do Some Checking.
$ cat /etc/redhat-release
$ cat /etc/issue
Those commands should return the information that you are running Mageia4. I did have an issue on one machine and $ sudo urpmi mageia-release-commonfixed it. You can also edit these files to change the version number.