How to change account information after a PO is approved and transferred to GL?

Hi Everyone,

I have a PO question.

Situation:

     -  PO is approved and transferred to GL, but one of the lines got wrong year.

     -  It has two lines, one needs to be changed and without matching to any invoices.  The other line has one invoice with payment.

     -  Both lines are greyed out when PO is open.

Question: how to change the first line if not to cancel the invoice/payment?  Close the line and enter a new one?  Please advise.

Thanks,

Ning