sudo apt update && sudo apt dist-upgrade sudo do-release-upgrade
sudo apt update sudo apt upgrade // Prepare the 16.04 system for release-upgrade do-release-upgrade // 16.04 to 18.04. The system will prompt you for a password sudo apt update sudo apt upgrade // Check for errors. Stop if there are errors. do-release-upgrade -d // The -d is required until August 13, 2020 when 20.04.1 // is released. After that, DON'T use -d.