Go to Discussions.
Select the Discussions tool from the site Tool Menu.
Select Delete Forum from the More dropdown menu.
Select the More link next to the forum to delete, then select Unrecoverable Action: Delete Forum option from the dropdown menu.
Alternatively, select Forum Settings next to the forum to delete.
Scroll down to bottom of page and select Delete Forum.
Confirm deletion.
To proceed, select Unrecoverable Action: Delete Forum to remove the forum from the site.
Deleting a forum will remove the forum and everything associated with it, including all topics and conversations.