If you want to add and manage payment methods you can do it in your profile settings. If you add a new card you will have it as an option to make future contributions.
Note: Updating your payment methods here does not change the card which your contributions are currently being made with.
If you want to change the payment method of one of your subscriptions you have to head to your “Subscriptions” page (opencollective.com/subscriptions) log in with the alias you used, cancel the subscription and do a new one with the desired card and amount.
To manage your payment methods, saved cards, follow this instructions:
Login with your email, and head to your profile.
Click “EDIT PROFILE” to access options:
Head to payment options and click on “add another payment option”:
Fill out your new card details and click "save: