If you need to change the credit card you're using to pay for your Topspin account, all you need to do is let your existing payment schedule expire and re-upgrade with a new card. Here's how to do this:
1. Disable Auto-Renewal on your Live Receipt:
When you first upgraded your Topspin account, you received a receipt detailing your initial billing, which contained a link to your live receipt. (You can also get to that in your Artist Profile).
Your live receipt contains an Automatic Renewal feature that can be toggled on and off. Click the auto-renew button to ensure automatic renewal is disabled, like so:
2. Re-upgrade with your desired credit card
Basically, when your paid access expires (your expiration date can be found on your receipt, as pictured above), you'll be notified that your paid membership has expired, and you'll be free to re-upgrade your account if you wish. At that time, just enter whatever payment card you'd like to use heading forward. Nothing in your account will be harmed or removed while your account sits in Free Trial mode waiting to be re-upgraded.