How do I delete a topic?
Go to Forums.
Select the Forums tool from the Tool Menu of your site.
Select Delete Topic from the drop-down menu.
Select the More link next to the topic you want to delete, then chose the Unrecoverable Action: Delete Topic option from the drop-down menu.
You will be prompted to confirm the deletion. If you are sure that you want to delete the topic and all of the messages within it, select the Unrecoverable Action: Delete Topic button.