Q:

How to eliminate/deactivate Ubuntu One account? 

I want to eliminate my account since I created it only as a trial. 

A:

From the FAQ
How do I downgrade or cancel my Ubuntu One account? 
Do you want to either downgrade or cancel you Ubuntu One plan?  Both the downgrade and cancel options are available in the Account area.  Click on "View/Edit" and you will find links to downgrade or cancel your subscription. 