Despite the fact that the final version of Ubuntu 16.04 Xenial Xerus LTS has not been released yet, some users may want to try the beta release.
Because Canonical provides an official upgrade path, upgrading your Ubuntu system (Ubuntu 15.10 Wily Werewolf or Ubuntu 14.04 Trusty Tahr) to Ubuntu 16.04 Xenial Xerus LTS Beta is easy.
All you need to do is perform a regular system upgrade:
$ sudo apt-get update
$ sudo apt-get dist-upgrade
Install the update-manager-core if it is not already available, and run the upgrade:
$ sudo apt-get install update-manager-core
$ sudo do-release-upgrade -d
Without any argument, the d-release-upgrade command looks for the latest stable version of Ubuntu available, but -d tells the upgrader to include the unstable versions also.