To upgrade on a server system:
- Install update-manager-core if it is not already installed.
- Make sure the Prompt line in /etc/update-manager/release-upgrades is set to ‘normal’ if you are using 19.10, or ‘lts’ if you are using 18.04 LTS.
- Launch the upgrade tool with the command sudo do-release-upgrade on 19.10; use sudo do-release-upgrade -d if you are using 18.04 LTS.
- Follow the on-screen instructions.