One of those lines is the name of the site, and the other is the name of the page you are looking at. By default, teachers get one page inside their site and both have their own name on it. We can't remove one of those at this time, but you can rename the page if you wish.
As a webmaster:
- Click into Site Center
- Click Tools
- Click Manage User Sites
- Click the teacher's name (if you can't, it's because they haven't published a site yet.)
- Click Properties
- Change the title and click Submit
At this time you can't change the title of the site (the section title), but this will come in a future update.