There are several ways. Right-click on the clip, and select Rename (Ctrl+R). Or, use the Edit | Rename Title (Ctrl+T) menu. Or, you can right-click on the clip and select Properties, and edit the tile in the property dialog. Or, you can highlight some of the clip in the Preview/Edit pane, right-click, and choose "set as title".
You can also have the title reflect changes made during editing. See Tools | Options | Editing, and there's an option to change the title as the clips are edited.