Here are some the steps to follow when deleting old threads in the discussion board:
Full Answer
On the Thread Detail page, click the title of one of your own posts. The post appears in the Current Post portion of the content frame. Click Edit to modify the message or click Delete and confirm its removal.
You can edit posts in any thread. If a student added inappropriate or inaccurate content, you can edit the post. When you create or edit a forum, you control if students may edit their published posts. Open a forum and select a thread.
Open the discussion's menu and select Delete. You can delete an entire discussion along with all responses and replies. Instructors can delete any discussion, while students can only delete discussions they've created. When students delete a discussion, other users see a message about the deletion.
From the pull down menu select View Grade Details. 4. On the screen that appears, find the submission near the bottom of the screen. To the right of the entry, click the button labeled Clear Attempt.