To change the payment method associated with your subscription you would need to follow the below steps:
1. Login into your Twitter Counter account
2. On the left features panel click on "Settings" and select "Subscriptions"
3. Under "My Subscriptions" click on the "Show details" button. (Look to the right, it will be gray)
4. Scroll to the end of the page until you see :
5. Select "Change payment method" and enter a new payment method