You can edit the details of a Purchase Order by clicking on the Edit Pencil next to the name in Inventory > PO tab. 

This will take you to the PO edit screen. Here you can edit the following fields:

Field Name	Function
PO Number	Assigned when the PO is created. Cannot be changed.
Supplier Name	Enter in the Supplier Name here.
Status	Status reflects the current status of related stock that is part of this purchase order. It is a way of communicating the status to the stock tab on an active order that has been added to this PO. The status here will be part of the link on the stock tab. Clicking on this link will take you directly to the PO: The available statuses are: Pending Sent Received Received Partial
Notes	Any informational notes can be added here.