You can manage your Apple ID account directly from your device in the App Store or from within iTunes.
Please follow these steps to amend your account from your device:
1. From your device's Home screen, tap App Store.
2. Tap Featured on the main navigation at the bottom of the screen.
3. Scroll to the bottom of the page.
4. Tap the Apple ID button in the lower-left corner. (If you are not signed in, tap the Sign In button, and sign in with your Apple ID. Then, scroll back to the bottom of the page, and tap the Apple ID button.)
5. Tap the View Apple ID button.
6. Enter your password and tap OK.