1. Navigate to the Courses tab
2. Select the name of the course
3. Select the People sub tab
4. Select the box next to the names of the people to extend the due date for
5. Select "Extend Due Date" from the "Perform a bulk action on selected people" dropdown menu on the right, a new window will pop up. 
6. From the dropdown select None, A Time Span, or A Specific Date.
7. Select either the number of Days or Weeks (for A Time Span) or select a due date on the calendar (for A Specific Date).
8. Select Update.

Note:  Changes to the due date may take a few minutes to appear for the selected people and you may need to refresh the page to view the change.

Note:  Due Date will only be available in the dropdown menu if you have a Due Date set in the course settings.