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?
This is actually a question I’d like some opinions on!
I have a ton of headless servers running Debian that I just replace the sources.list for an upgrade. I imagine things are much more complicated when switches like X11 to Wayland happen, so all desktop environments get a wipe/install instead… But maybe I’m just making a lot of work for myself doing that!
Nah, regular upgrades should be fine for those too.
Wayland and X11 can exist in parallel. I have multiple desktop environments with some defaulting to Wayland and some still using X11. For my casual machine, I use XFCE most of the time ( X11 ) but have been toying around with the new COSMIC ( Wayland ). I switch back and forth.
So, the X11 on your system will not hold you back when you move to Wayland. Of course, at some point the old stuff is just cruft. So you do have to do a bit of janatorial from time to time.
I use a rolling release.