We need more information In order for us to help you with this issue. Have you try to go to "Open Item List", select the item that you are having issues with and then click on the top, where it says "Edit"? You are going to be able to change the amount of this item from here. Please try , if the issue persist, open support ticket here:
http://www.nch.com.au/support/supportcontact.html?software=Copper&support