Originally Posted by
dlinsider
If you upgarde your voucher or ticket to a fully refundable ticket the original non-refundable amount still remains non-refundable otherwise everyone with non-refundable tickets would pay the difference to make them refundable and get all their money back
dlinsider is correct,
It has been tried by many, but it cannot be done.
In the case, the extra amount you actually paid for goes back to your credit card and the voucher amount goes back to a voucher.