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?
Well, yeah. Hard drive failure can force a reinstall. And with laptops there isn’t usually another place for a hard drive, from where to restore the system.
Brainfart, I said laptop meant desktop, obviously didn’t change the GPU on a laptop.
*Framework has entered the chat*