Rosters can be deleted from rooms. To start, click on Rooms. Next, find the room with the roster you'd like to remove and click on the Roster menu. A message will be shown to confirm that you'd like to delete the room. Click Yes to confirm. Any students that already connected will be logged out and taken back to the student login page.
Whether you're trying to add, edit, or delete a roster, if you have an activity running in the room, you won't be able to add/edit/delete a roster. You'll see the error message below:
To finish an activity, go to the Results tab in your account and click the Finish button. Check out this guide to help you on how to end an activity.