RDS12 r2 login.aspx how to change "domain\username" text to "email address"

When my user goes to domain.com/rdweb they are asked for "domain\user name" and password.  

My users can already login with their email address, i just need the page to tell them to use email address.  What line on the login.aspx page must i change to accomplish this?  I only want to chang the text "Domain\User Name" to "email Address", right next to where they would enter "username".

Thanks,

Brandon