Network Upgrade for Ubuntu Servers (Recommended)

   1.

      Install update-manager-core if it is not already installed:

      sudo apt-get install update-manager-core

   2.

      Edit /etc/update-manager/release-upgrades and set:

      Prompt=normal

   3.

      Launch the upgrade tool:

      sudo do-release-upgrade

   4. Follow the on-screen instructions.