Whatever payment you made before and hasn't been used towards a class, you will have that amount on your account. When you move to a new teacher, if you continue to have the same number of classes, then there will be no change in billing. However, if you have reduced # of classes, then you will receive a credit towards next month's bill. If you have increased number of classes, you will have to make a payment immediately. 

Just follow the process and steps in our system and you will be all set.