Upgrading an Ubuntu Server is quite easy, just follow the below commands:
Option 1: Tldr; (just run the below!)
sudo apt-get update && sudo apt-get upgrade
sudo apt dist-upgrade
sudo do-release-upgrade
reboot
Option 2: Follow the steps to Upgrade Ubuntu Server
1: Update the packages:
Start by making sure that you have all the packages and dependencies ready locally before we upgrade
sudo apt-get update && sudo apt-get upgrade
2: Update the dependencies for the distribution:
sudo apt dist-upgrade
3: Check for upgrade version:
sudo do-release-upgrade -c
4: Perform upgrade:
sudo do-release-upgrade
5: Reboot:
reboot