Upgrade Ubuntu 6.10 (Edgy Eft) to 7.04 (Feisty Fawn) to 7.10 (Gutsy Gibbon), then to 8.04 (Hardy Heron)

From 6.10 to 7.04:

sed -e 's/\edgy/feisty/g' -i /etc/apt/sources.list
apt-get update && apt-get upgrade && apt-get dist-upgrade

From 7.04 to 7.10:

apt-get install update-manager-core
do-release-upgrade

From 7.10 to 8.04.1:

do-release-upgrade