You need to read this: http://community.rtcamp.com/t/upgrade-to-14-04-and-receiving-python-error/5691
Apparently you first have to update EE and then do OS upgrade. But why would you nned to upgrade to ubuntu 16? Does it have something you need that your current OS doesn't provide? I still full of bugs so I don't see any reason to upgrade...
And next time please search the forum first before posting your question. You may find the answer 