Dynamics NAV - Removing Purchase Orders

First of all, according to this
https://msdn.microsoft.com/en-us/library/hh173005(v=nav.71).aspx

If the order is fully posted, both received and invoiced, then the purchase order is deleted.

So how do i remove old purchase orders?

1. Run the "Delete Invoiced Purchase Orders" routine
1. Search for Delete Invoiced Purchase Orders
2. Enter Range
3. Click ok
4. The system will remove all invoiced purchase orders
2. Another, more drastic method is to simply adjust the Qty Rcd not invoiced to 0, then manually delete the PO
1. This method should only be used if you are certain that there are no more invoices or receipts to be completed in connection with this transaction.
2. Manual inventory adjustments and GL journals will have to be done to fix any problems caused by using this method
3.    update [Purchase Line] set  [Qty_ Rcd_ Not Invoiced] = 0 where [Document No_] =   'PO000155'