The ‘main' archive of Ubuntu 18.04 LTS will be supported for 5 years until April 2023. Ubuntu 18.04 LTS will be supported for 5 years for Ubuntu Desktop, Ubuntu Server, and Ubuntu Core. Ubuntu Studio 18.04 will be supported for 9 months. All other flavors will be supported for 3 years.
Upgrading from Ubuntu 17.10 Desktop
Press Alt+F2 and type update-manager -c into the command box.
Update Manager should open up and tell you that Ubuntu 18.04 LTS is now available.
If not you can run /usr/lib/ubuntu-release-upgrader/check-new-release-gtk
Click Upgrade and follow the on-screen instructions.
Upgrading from Ubuntu 17.10 Server
Install update-manager-core if it is not already installed.
sudo apt-get install update-manager-core
Launch the upgrade tool with the command
Follow the on-screen instructions.
Note that the server upgrade will use GNU screen and automatically re-attach in case of dropped connection problems.