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