You can update your payment details (including credit cards) by logging into your Pusher account at https://dashboard.pusher.com/
You'll need the account details that were originally used to create the account, so if you're not the account owner you may need them to do this for you.
- Click on Account > Channels billing from the menu in the top right
- Scroll down the page and click the Update payment details button
If you can't do this or have further problems, please log a support ticket using the link below.