Can a judge in NY impose a retroactive increase in child support if I have been paying the court ordered amount

If your original court order was brought by the other parent, and they are not on public assistance, then any increase in your child support is retroactive only to the date that they file for upward modification, if they decide to do so.  The custodial parent for a child support order can file for upward modification only if your income goes up by 15% or if three years has passed since the date of the original order.  Then, you will only owe retroactive support back to the date that they file for that upward modification.