Ubuntu -bash: do-release-upgrade: command not found

Originally published at: https://www.cyberciti.biz/faq/ubuntu-bash-do-release-upgrade-command-not-found/

I am using Ubuntu Linux 16.04 LTS cloud server. I followed this page to upgrade Ubuntu 16.04 to 18.04 but, I am getting an error that read as ’ -bash: do-release-upgrade: command not found.’ Why am I not getting the Ubuntu 18.04 upgrade using do-release-upgrade and how do I fix this problem?