On the Loan Payment Screen, you want to select the loan you are wanting to discount, Once you have done that you want to enter the full overdue amount, then

When your at the New Sale Screen, Enter the Stock Number you are wanting to discount Click the item you are wanting to discount, so it highlights Red, Then Click

At the Home Screen you want to Select number Four, like the photo below, And Type in the stock number that you are wanting to change the price of and