Change Primary Exchange in the ADS

I have two exchange running under the same domain,
when i go to create a new user for the domain, the defualt exchange that the ads picks up for the user is EXCHANGE_1, i have to select EXCHANGE_2 from the drop down during the wizard is guiding me through the steps of creating the user.
How can i change the settings such that, when ever i create a new user, the default exchnage that shows up is EXCHANGE_2 and not EXCHANGE_1.

Thanks alot.