You can manage your Couchsurfing subscription on your Membership & Contributions page within your Account Settings. You can click here to get straight there. On this page, you can view your subscription details, update your payment method and cancel your subscription.
Here are some additional articles that might be useful:
How do I change my payment details?
How do I cancel my Couchsurfing subscription?
Can I join Couchsurfing again after having canceled my subscription?
Upgrade your account with Verification and make your profile stand out. Get Verified today!