Change the email address of the default user when creating a new virtual server

How do you change the email address of the default user when creating a new virtual server? I've was able to add a new user/email account but I couldnt find a way to change the Administration username account and alias. For example when creating a new virtual server the default email created is based on the Administration username created so it would be acme@mydomain.com if the custom Administration username name is acme.

I want to be able to edit these settings so that the Administration username and account is something that makes more sense like webmaster@mydomain.com instead of acme@mydomain.com.

How do I accomplish this?