Q: How do I update credit card info?

http://support.apple.com/kb/HT1918

Forum Tip: Since you're new here, you've probably not discovered the Search feature available on every Communities page, but next time, it might save you time (and everyone else from having to answer the same question multiple times) if you search a couple of ways for a topic, both in the relevant forums and in the Apple Knowledge Base before you post a question.

Regards.