Delete a forum
Go to Forums
Select the Forums tool from Tool Menu in your site.
Click the More link next to the forum you want to delete, then chose the Delete Forum option from the drop-down menu.
You can also click Forum Settings next to the forum you want to delete
Deleting a forum will remove the forum and everything associated with it, including all topics and conversations. If you are sure you want to delete the forum, click Delete Forum to remove it from the site.