You can partially or fully prepay your loan at any time with absolutely no prepayment penalty or fee.
Any payments made in addition to your contractual monthly payment will be applied towards a reduction in the principal balance of your loan. Additional payments towards your principal balance allow you to repay your loan early by reducing the total amount of interest you'll pay. A full prepayment of your outstanding principal balance, plus any accrued interest or fees, will pay off your loan and bring an end to your monthly payments.