Deleting Discussion Topics and/or Categories
Step 1: Under Course Tools, select Discussions (see figure below). Note: You must be in the Teach Tab to delete discussion topics and/or categories.

Step 2: Select the check box next to the discussion category and/or topic(s) you wish to delete, and click the Delete button (see figure below).

Step 3: When the warning message appears (see figure below), click OK to delete the category or topic.