How can I change my iTunes / App Store password?
You must change your iTunes password (otherwise known as an Apple ID) on a computer. Apple does not currently provide a way to change iTunes or App Store login passwords directly on iOS devices. To change your password follow these steps:
1. Open a web browser and navigate to appleid.apple.com
2. Select Manage your account under "Already have an Apple ID?"
3. Enter your Apple ID and current password and click Sign In
4. From the left menu select Password and Security
5. Click the Change Password link under "Choose a new password."
6. Enter your old password followed by the new password twice
7. Click the Save Changes button
Once your Apple ID password has been changed, you'll have to enter the new password on your iOS devices and in iTunes on your computer to use the iTunes store.
Enter the new password on your iOS device by navigating to Settings -> Store -> Apple ID
Enter the new password in iTunes on your computer by navigating to the top menu Store -> Sign In