Welcome to the BbSupport Forums
There isnt currently away for an admin to delete their board, but you can just delete everything or hide everything and go to your admin area, edit board settings and put on the MBA setting so no one but mods and admins can access your board. the board will eventually get deleted when the free boards on your server get deleted.
We are no longer allowing new communities to be added to the network, but we can rename your current boards URL if the desired name is not taken yet.
Email us at firstname.lastname@example.org
from the Admin Username's registered email, telling us the exact URL you want and give a ok for it (naming the old URL) to be renamed.