It is possible to upgrade Ubuntu versions 18.04 and 19.04 to the latest version 20.04 using the command line. Before starting with it, we advise taking the backup of your important data. Here are the steps for doing the upgrade.

1. Login to the server as root and take the necessary backup of your data and store locally or any other safe place.
2. Check the current Ubuntu version:
   
   # lsb_release -a

3.Upgrade all installed packages on the current version:

# apt update
# apt list --upgradable
# apt upgrade

4.Once the upgrade process is completed, reboot the server:

   # reboot

5.Once the server is rebooted, login as root again and install the update-manager-core package.

# apt install update-manager-core

6.Once installed, run the upgrade command as below:

# do-release-upgrade -d

7.The command will ask for some confirmations and you need to respond to it as per the notifications on the screen.

8.It will take 10-15 minutes to complete the process. Once the upgrade is done, you will need to reboot the server.

9.Once rebooted, log in again and double-check if the upgrade is done well and verify the version as well.