Changing Default Email Address Exchange 2013

I need to change the default email address. I'm setting up the John Doe account as JDoe@example.com. However, if there are other John's in the directory it will append a number to it and set that as the default. So now I have John2@example.com. It does also add the JDoe@example.com, but when the user replies to an email it comes from the default John2@example.com. I know how to do this in Exchange 2010, but don't see the option to do it in Exchange 2013.