Your Apple ID controls everything you do through your device from enabling iCloud to shopping on the iTunes store. You can manage your Apple ID by visiting https://appleid.apple.com. This page will allow you to edit your Apple ID information, recover your Apple ID in case you forgot it, or reset your password.
The 'manage your account page' will give you access to:
Name, ID, and Email Addresses
Password and Security
Language and Contact Preferences
You will of course need to know your Apple ID and password to access this information and edit it.
You will have to sync your iOS device after you change any information by navigating to Settings -> Store -> Apple ID.