This article talks about how to update your current ubuntu old version to ubuntu 21.04 beta version without reinstalling Ubuntu.
If you are looking for a development version of Ubuntu 21.04 then follow this command:
update-manager -d
After the Software Updater finishes checking for updates, it’ll show you a message that reads.
The software is up-to-date. However, Ubuntu 20.10 is now available (you have “your Ubuntu version”)
Click on upgrade. The process might take 30-45 minutes to complete depending on your internet’s speed.
Download the latest Ubuntu 21.04 beta build here