clean install: you make a backup, nuke the computer, install a fresh upgraded copy of the distro you want from a live usb, copy your data again to the computer.
upgrade: you wait ‘till the distro’ developers release an upgrade you can directly install from your soon to be old distro, you use a command like sudo do-release-upgrade
and why do you upgrade like that?
Try out immutable distros like NixOS: that is stunning in upgrading.
'73
I tried once. Could not figure it out. I’ll leave that to the young people.