Entering Negative figure in Quantity in stock : Sage line 50

Hi,

In sage line 50, There is a product list, Under product list there is Quantity in stock and free stock Menu. Some of my free stock are negative (Exa: - 450) where quantity in stock is 0. How to fix it................ Can i make quantity in stock - 450? I could not find how to do negative enrty in quantity in stock. Is there any body can help me?

Thanks

kind Regards

Abdur