First Verify the version of Ubuntu that you are running:
sudo lsb_release -a
$ sudo apt-get update $ sudo apt-get upgrade $ sudo apt-get install update-manager-core
Update Jaunty 9.04 to Karmic 9.10 update /etc/apt/sources.list and replace "jaunty" with "karmic" $ sudo apt-get update $ sudo do-release-upgrade if do-release-upgrade is not working just do a apt-get upgrade
Update Karmic 9.10 to Lucid 10.04 update /etc/apt/sources.list and replace "karmic" with "lucid" $ sudo apt-get update $ sudo do-release-upgrade if do-release-upgrade is not working just do a apt-get upgrade
From Version 10.04 to 12.04 the Upgrade Get easier:
All you have to do is run the following command:
sudo do-release-upgrade
and follow the prompts.
Useful Links
List of Ubuntu Releases
http://en.wikipedia.org/wiki/List_of_Ubuntu_releases
How to update Ubuntu server from 9.04 to 10.04
http://thanhsiang.org/faqing/node/156
Lucid to Maverick
http://www.ubuntugeek.com/how-to-upgrade-from-ubuntu-10-04-lucid-to-ubuntu-10-10-maverick-desktop-and-server.html