Xcode 4 introduces schemes which provide all the options on how to build/run/profile/etc. your application. You can change the active scheme using the Scheme drop-down button at the top of the project window and/or edit the scheme via Product > Edit Scheme… ⌘< menu item. Then on the left source list, you can select the Run item, and in the Info tab in the right pane you can choose to use the Release configuration in the Build Configuration drop-down.