Your Malwarebytes Premium subscription automatically extends prior to its expiration date when your subscription is set to automatic renewal. The payment goes through the associated credit card on your account.
If your license is set for manual renewal, you will receive renewal reminders at least 30 days prior to the expiration date. These emails contain instructions on renewing your subscription. Once you manually renew a license, the automatic renewal reactivates.
For more information, see Renew subscription before automatic renewal date.