You have to change that in each Collection's Edit view (search for the "Sort on" field). Have a look at: http://docs.plone.org/working-with-content/using-collections/newstyle/creating_collections.html
You have to change that in each Collection's Edit view (search for the "Sort on" field). Have a look at: http://docs.plone.org/working-with-content/using-collections/newstyle/creating_collections.html