Click the Community side-tab and click Discussion Board. The Discussion Board opens.
Use the fields in the search window above the results table to locate the appropriate organization.
Click the discussion board graphic 
corresponding to the appropriate discussion board. You can also double-click the discussion board name or select the discussion board and click View Details. When you select a discussion board, the window changes to show the topics that are currently being discussed on the discussion board.
Select the appropriate topic to expose the replies in the topic.
Click the delete 
graphic that corresponds to the topic that you want to delete.