When workspaces are no longer relevant, they can be deleted by a Team owner. To do so, click the
v icon beside the Team name in the blue header bar and select "Workspaces."
Once on the Workspaces page, click "Edit Workspace."
In the Edit Workspace dialog, click the red, "Delete this workspace" link at the bottom of the window.
This will take you to a confirmation form where you must enter your password before clicking "Delete Workspace" to confirm the deletion. Deleted workspaces cannot be recovered so be absolutely sure you want to delete them before doing so.