You can change your account ID, password, or billing information at any time.
To change your account information:
Choose Store > View My Account.
Your changes take effect immediately.
If you have an Apple account, changes you make in iTunes are also recognized by other applications in which you use the same Apple account.
If you have an AOL account, changes you make in iTunes don’t affect your AOL account on the AOL service. For example, if you change your password in iTunes, the password you use to log in to the AOL service does not change.