Problem with confirmation of ship

We have an shipment that was confirmed with charges (freight) in the amount of 
6 billion dollars. Obviously this is incorrect. I immediately created a credit 
to offset this invoice, but we are having problems with a few custom reports 
that are unable to calculate such a large number. I need to know if it's 
possible to change that freight amount now that the order has been confirmed. 
Is there a file that can be changed using my data base utility or would you 
need to change multiple files?

Also, once the original invoice has been changed, we would need to change 
credit as well.

Can anyone help with this?

Karen Smith
Allen Engineering Corporation