iPhone - Apple ID - Where do I manage my Apple ID email / password?

Apple uses your individual Apple ID to authenticate purchases, authorize computers to play content and determine where to send important information such as invoices. Your Apple ID can be used for services in iCloud, the iTunes Store, App Store, iBookstore and iChat.

Full control over managing the Apple ID takes place on a computer. To access your Apple ID account information and profile navigate to the following web address:

http://appleid.apple.com

Choosing 'Manage your account' from the right side of the screen will prompt for the current Apple ID and password for access. From here, a list of options is presented:

Name, ID, and Email Addresses

Password and Security

Addresses

Phone Numbers

Language and Contact Preferences

Don't forget that if you change your Apple ID or password you'll have to update any iOS devices or iTunes accounts on your computer to reflect the new information.

Enter new Apple ID information on your iOS device by navigating to Settings -> Store -> Apple ID.

Enter new Apple ID information into iTunes on your computer using Store -> Sign In.