Upgrading from a physical CD

sudo apt-cdrom add
sudo apt-get update && sudo apt-get dist-upgrade

Upgrading from an ISO image

sudo mount -t iso9660 ubuntu-6.10-alternative-i386.iso /cdrom -o -loop

sudo apt-cdrom -m add
sudo apt-get update && sudo apt-get dist-upgrade
sudo umount /cdrom

** must use full path for the ISO image
** may also need "-y" and "--force-yes" options