LeanKit's step-by-step guide on how to permanently delete a board.
You can delete a board if it is no longer in use and you don't need to retain any archived historical data from that board. Deleting a board removes it entirely from your account; the data from the deleted board is no longer available, even among your archived boards.
To Delete a Board:
On your organization's LeanKit home window, click on the white triangle on the left side of a board's preview image. Make sure you click on the board you would like to delete. From that menu, select Delete.
You with be asked to confirm that you want to delete this board, which will result in the removal of all board-related data.
Click Yes to confirm and delete the board.