Here is the way through which you can upgrade your Ubuntu from older to the latest 20.04 version.
Running Ubuntu update
Make sure that your system is up-to-date before you start anything.
Update your Ubuntu completely then upgrade with Apt.
Run the following commands one-by-one to start the upgrade process:
$ sudo apt update
$ sudo apt upgrade
$ sudo apt dist-upgrade
Before you begin to upgrade you Ubuntu from 19.10 to 20.04 you may need to remove all the unwanted and no longer required packages with the help of this:
$ sudo apt autoremove
Ubuntu has developed its own automatic way of upgrading. You no longer have to keep your eyes on the process, you just have to put it on upgrade and Ubuntu will handle the rest by itself.
Upgrades from 19.10 will not be enabled until a few days after the release of 20.04.
Upgrades from 18.04 LTS will not be enabled until a few days after the release of 20.04.1 which is expected in late July 2020.
There are no offline upgrade options for Ubuntu Desktop and Ubuntu Server.
You have to install one package if you want to take this route.
$ sudo apt install update-manager-core
After it is over, run the Ubuntu upgrade utility.
$ sudo do-release-upgrade
If you are doing this too soon or before the availability of the new release, it will tell you that there is
"No new release found".
In that case, if you still want to continue the process, add the
-d flag (at your own risk) at the end of the command to force the upgrade.
$ sudo do-release-upgrade -d