As a friendly recommendation:
If it was about me, I would encourage to backup the home directories as well as mail or similar, depending what other kind of services running under the particular system.
Backup the data to an external usb drive or the whole source drive if you are keen on that, for example. Then do a "clean" install of a new system on the original drive. Otherwise you might run into issues, where you might miss out on an important package, if you snapshot upgrade one by one.