Icloud Updates
How do I change my icloud email and password?
iPhone 4S, iOS 7.0.4
You wouldn't be able to change your primary @icloud.com address, but you could add an alias at www.icloud.com > Mail > Preferences. If you have an other email address e.g. @gmail.com, @outlook.com then you could change that at https://appleid.apple.com (where you by the way also can change the password.
But before you change your email address please make sure to deactivate "Find My iPhone" (Activation Lock) from all your devices (e.g. iOS: Settings > iCloud > Find My iPhone), otherwise you won't be able to update or delete your account later.