GST Amount

We have just upgraded to NAV 2013 from 5.1.

I noticed a change in the system and not sure how we need to adjust.  IN the old system ont he statistics it was possible to change the GST Amount in the statistics of an order (e.g. Purchase Order).  However in the new system, the VAT Amount Line table is non existant, and the only occurance of the GST Amount field is not editable.   Is this a change in the Australian localization, or perhaps our own customizations in the old system, I am not sure.  Any thoughts appreciated.