Move all items within every shared folder into a standard (non-shared) folder.
Delete the (now empty) shared folders (go to Sharing Center in the left navigation → Manage Shared Folders → click the Delete icon and click Yes to confirm).
Purge the deleted shared folder (go to Sharing Center in the left navigation → Manage Shared Folders → check the box to enable the View Deleted Shared Folders option → click the Purge icon and click Yes to confirm.