The supported upgrade path from Ubuntu 8.04 Desktop is via Ubuntu 10.04 Desktop. Instructions and caveats for the upgrade may be found at
Lucid Upgrades. Ubuntu 8.04 Server continues to be actively supported with security updates and select high-impact bug fixes. All announcements of official security updates for Ubuntu releases are sent to the ubuntu-security-announce mailing list, information about which may be found at https://lists.ubuntu.com/mailman/listinfo/ubuntu-security-announce.
Since its launch in October 2004 Ubuntu has become one of the most highly regarded Linux distributions with millions of users in homes, schools, businesses and governments around the world. Ubuntu is Open Source software, costs nothing to download, and users are free to customize or alter their software in order to meet their needs.
Ubuntu Release Manager