I have the same problem and I didn't want to install that bulky iTunes on my Windows. Here's what Apple has on its website.
Changing your account information using an iOS device:
From your iPad's home screen:
- Tap Settings
- Locate and tap iTunes & App Stores on the left margin.
- Tap on your Apple ID. (If you are not signed in, enter your Apple ID and password, and tap Sign In.)
- Tap View Apple ID (then wait for like, forever).
- Enter your Apple ID password.
To update your name, billing address, or payment information, follow these instructions:
- In the Edit section, tap Payment Information.
- Update the information that you want to change.
- Tap the Done button when finished.