HOWTO - Cancel Direct Posting Remaining Quantity

Louis

Hi,

My Case :
A Sales Order exists with <direct posting> for QTY 2,5.
A corresponding Purchase Order is linked with QTE 2,5.
A partial delivery has been validated for QTY 1,5.

The remaining ordered quantity will never be delivered...

Is it a way to avoid the message
'You cannot change Quantity because the order line is associated with purchase order..."

Howto change the remaining order quantity (Filed QTY) to cancel the remaining QTY and close the orders (Sales and Purchase) ?

TIA,
L