Only authorized users have the permission to change the navigation menu. If you are responsible for some part of the site, eg for a group's or project's web pages, and want to change the navigation menu, you should contact [2] our web master and ask for the proper permission setup.
Once you have the proper permissions you can add a menu item by submitting (or editing) a page and indicating the correct parent menu under 'Menu settings'. For security reasons, it is currently not possible for normal users to remove a menu item, please contact a web master to do this for you.
Links:
[1] http://qurope.eu/users/ltheussl
[2] http://qurope.eu/contact
[3] http://qurope.eu/faq/web-site-management-submit-edit-pages-etc