In addition to consolidating the various editing icons into one drop-down menu, Moodle 2.6 changed the way you edit the heading for a topic area. Under Moodle 2.5 and below, you clicked on the familiar yellow pencil under that topic heading to edit what Moodle calls the "Topic Summary". Under Moodle 2.6, that yellow pencil icon is replaced by an icon of a gear on top of a piece of paper, marked by a red arrow in the image below:
When you click on that "Edit summary" icon, you are taken to the familiar "Summary of Topic #" dialog box. To edit the section title so that something else appears besides "Topic 1" or "Topic 2," etc., you need to "de-select" – in other words, remove – the check mark that appears in "Use default section name," and then you can type in a new title:
Once you have typed in that new title, scroll down to the bottom of the page, and click on the "Save changes" button. Your topic will now have a new title: