I downloaded the iso installation file for 12.10 from the website and attempted to install. However, the option to upgrade from the existing installation of 12.04.1 is disabled, and the only choice allowed is to erase the existing installation and install fresh.

Of course, I am aware that I can upgrade using the distribution upgrade tool from within 12.04.1, but my problem is that the files take forever to download despite me running it off a 12 mbps connection. I need to upgrade on 4 more systems and I'd hate to have to download and upgrade via the upgrade tool on each one.

Can anyone help? Is there anyway to just use the 800mb iso file that I have downloaded off ubuntu.com without having to wipe out all my files?