The first consideration to make, is to make sure the accounting practices at your school allow for a credit from one academic school year to be transferred to another academic school year. If this is an acceptable practice, use the following procedure.
1.  Navigate to

2.  Go to the past school year with the credit balance.

3.  Go to the family account. 

4.  Apply a fee to the family account in the same dollar amount as the credit . This will $0 out the credit balance in the old year.
           5.  Apply a discount in the new school year with the exact dollar amount of the fee applied in the prior year.
                                 How do I add a new fee or discount in edit billing details?
Note: It is best practice to give the fee in the prior year and the discount in the new year similar names.

For example, "2016-17 Credit Balance Transferred" (in the old year) and "2016-17 Credit Balance Transferred" (in the new year).