Ubuntu 7.04 is the current stable version of the Ubuntu operating system. The common name given to this release from the time of its early development was “Feisty Fawn”.
Before Upgrading You need to remember the following point
Take comple backup of your server before upgrading Now you need to upgraded Ubuntu Edgy Server to Ubuntu Feisty.
You have to update the sources.list file to apt-get be able to find the update-manager-core package
sudo vi /etc/apt/sources.list
and Change every occurrence of edgy to feisty
deb http://archive.ubuntu.com/ubuntu/ edgy main restricted
deb http://archive.ubuntu.com/ubuntu/ feisty main restricted
Update the new lists of packages by doing
sudo apt-get update
sudo apt-get install update-manager-core
Launch the upgrade tool
Follow the on-screen instructions