While being logged in as root, you’ll have to edit the file /etc/update-manager/release-upgrades and set the value prompt to normal.

vi /etc/update-manager/release-upgrades
set  prompt=normal

The update process will update your server to every single releases of Ubuntu (200MB download for each step and a restart required)

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

You are now on Ubuntu 10.10 Maverick Meerkat run one more time:

do-release-upgrade

You are now on Ubuntu 11.04 Natty Narwhal run one more time:

do-release-upgrade

to finally enjoy using Ubuntu 11.10 Oneiric Ocelot!

Ubuntu version names

• Ubuntu 11.10 – the current stable version, released in October 2011, codenamed Oneiric Ocelot.
• Ubuntu 11.04 – previous version, released in April 2011, codenamed Natty Narwhal.
• Ubuntu 10.10 – previous version, released in October 2010, codenamed Maverick Meerkat.
• Ubuntu 10.04 LTS – the current long term support version, released in April 2010, codenamed Lucid Lynx.