No problem at all. You can downgrade (e.g. weekly > biweekly) or upgrade (e.g. biweekly > weekly) at any point. Simply let me know during one of your lessons or by sending me a message or email, and I will change or cancel your subscription accordingly.
I do ask that you let me know at least 10 days before the next month starts. However, I am a decent human being so I will not let you pay for another month if you do not actually want more chess coaching. So please do not worry about this being a subscription, it is just for the purpose of the payments being automated - neither you nor I have to think about it again.