In this page:

demo.joomlaxtc.com/ecospa/index.php?option=com_k2&view=item&id=67&Itemid=307%22

how do I remove the right column as shown here:



what parameter in K2 and where should I change that ?

That looks like a custom template override for K2.
You can copy the override and edit it so show and display like you wish, or if you simply want it not to show you can search for .itemAuthorsplitwidth in the css and add display:none