From alpha,beta or RC now you can update the *.iso image to upgrade the OS, instead of downloading the entire iso image
Very useful for people with low bandwidth
Feels very much similar to `wget -c`
zsync is the name, upgrade is the game.
Here is how to do that :

<b>
sudo aptitude install zsync
mv ubuntu-9.10-rc-desktop-i386.iso ubuntu-9.10-desktop-i386.iso
zync <url>
</b>
 
Select the URL from the <b>file attached</b>