Sorry - neglected to resize the pictures, but hopefuly they still make sense. From the installed products page, click the 'settings' button on the top right. In the settings window that appears, click the 'change product listing' button. Next, from the manage product listings window, click the 'add' button and browse to the 7.1 beta xml file (which should have been included in the ITMS beta install zip file). Once you've selected that and retured back to the product listings window, make sure the new beta file is selected and click ok, then ok again to return to the installed products page. From there you should see all of the available installs.