Consider what "clean install" means, vs.
"Clean install" usually means "wipe it out and start over," either with the whole hard-drive or at the very least with the system-level materials. Usually
that's not what you want to do, or have to do. ("This isn't Windows, you know..."
"Upgrade" is a distro-vendor-supplied process, of some kind or another, that seeks to replace the outdated materials on your system with newer versions, while keeping as much of your existing settings as possible. Because of the latter consideration, no, the outcome won't be the same.
Generally, an upgrade goes through these steps:
- You buy, or else download-and-burn, a distribution DVD from the vendor of the distro you're using.
- You might be told to mount that disk and run some kind of preliminary setup-program on it.
- Then, you're going to be asked to reboot the system from that DVD. At this point, a special version of Linux is going to start-up, running entirely from the DVD drive, specifically so that it can mount your hard-drive as "an ordinary disk." (In other words, since "everything essential to running Linux" while in this mode is located on the DVD and not on your hard drive, it can replace whatever files it needs to on the hard drive without worrying about crashing itself.)
- The upgrade-process starts moving files around, installing new files and so-on while you go to lunch.
- The DVD is ejected and you're told to remove it and then reboot.
- Upon reboot, additional setup-stages might be carried out and you might be told to reboot once more. "You're done."
Now, there may still
be some adjustments that you'll still need to make, even after the upgrade is done, but this is almost-certainly the procedure that you'll want to use.