If you pay more than your fixed monthly payment, remaining funds will first be applied to any accrued interest from fees (if applicable), then to your principal loan balance. This can reduce the total number of monthly payments you'll have to make, and can reduce your next monthly payment amount.
If you are on automatic payments, making additional payments will not reduce the amount of your next monthly payment, but can reduce the total number of monthly payments you’ll have to make. Your automatic payments will continue to be withdrawn on your scheduled monthly due date, at the fixed amount agreed to in your loan agreement.