The content manager is able to change Shop Departments and the navigation items to the right of the Shop Department Menu using store experience.

Find a Branch and Sing In/Register can not be modified in the Admin tool, these would need to be changed with dynamic styles or by a developer in the page template.

The items displayed under the Shop Department menu from the catalog the user is seeing.  The Shop department' structure is used from the catalog. For more information on this refer to Configuring a Catalog

Editing Main Navigation

Navigate to: CMS > Managing the Store Experience > Header Navigation

In order to add new page links to the header, you can set the SEO Friendly Url in the content page section, and use the same URL to add it to the header navigation links.

You can use the SEO-friendly URL of your choice in the URL field, this should match what is set on the content page. Your new page will show up in your webstore in the following area, depending on how you set your display order.

Note - In order to see the pages on the webstore, the Administrator needs to Publish the Store experience.