How to Associate a New Email with iMessage on Your Device
1. Everything you need to do lives in the Messages tab of your iPhone, iPad, Settings,launch Settings and tap on Messages.
2. By default, iMessage is set to receive messages via your Apple ID email address and, if you have an iPhone, your phone number.
You cannot remove an email address until you've replaced it, so from the Messages setting, tap "Receive At" go to add Another Email.
3. Type in the new email address you'd like to associate with that device.
4. Apple will send a verification email to that address. When you receive it, just click the activation link and the new address will now be linked to that device.
5. Finally remove the original email by tapping the email address to remove .