'To Supplier' Attachments file does not sent updated version of files

We created a Standard Purchase order and Communicated to the Supplier through 'PO Output for Communication'. Later there was a change in Terms & Conditions, so we deleted the header level attachment, added the new attachment and re-communicated to the Supplier. At this time system does not pick the updated file attached from PO Header, and still communicates the old file.

Kindly advice, how to change PO Header 'To Supplier' attachment once communicated to the Supplier?