How To Upgrade From Ubuntu 12.04, Ubuntu 12.10, Ubuntu 13.10 To Ubuntu 14.04 Beta 2 :
The easiest way to upgrade from previous versions of Ubuntu to Ubuntu 14.04 Final Beta is via the command line.
Just install the update-manager-core tool, if it is not already installed:
$ sudo apt-get install update-manager-core
Next, start the upgrade process and follow the graphical instructions:
$ sudo do-release-upgrade -d
Note: Because do-release-upgrade -d has the -d argument, it upgrades to the newest under development Ubuntu release, for now Ubuntu 14.04 Beta 2.