How To Upgrade Ubuntu To 20.04 LTS Focal Fossa -

Run your Ubuntu Update

Before you do anything, make sure that your system is already up-to-date. Run a full Ubuntu update and upgrade with Apt.
$ sudo apt update 
$ sudo apt upgrade
$ sudo apt dist-upgrade
This will help to ensure that the difference between packages is as small as possible. It also will be the way that Canonical has most likely tested the upgrade themselves, so it's least likely to encounter bugs. Lastly, before you begin to upgrade Ubuntu to 20.04 LTS Focal Fossa you may also want to remove all no longer required packages using:
$ sudo apt autoremove