When you click to Edit the Section, the navbar is controlled by this area of the page
Attachment 151395
If you are talking about adding non-articles/non-sections to the sub-menu, then you would need to modify the template directly.
To find the template to modify, do this - vboptions > General Settings > Add Template Name in HTML Comments > set to Yes . Then go back to your page and view the source code and you will see the name of the template called around your part of the code. (Sometimes the template is the one mentioned at the very top of the page source.)