We've just released Android Studio 0.4.2, which fixes an important bug related to building projects found in 0.4.1 released earlier today.
If you are already running Android Studio, just restart it, or manually check for updates via Help > Check for Update... (on OSX, look in the Android Studio menu). This will download and install a small patch rather than download a full IDE image.
If you need to download a full install, visit the Android Studio Canary Build 0.4.2 page.
If you run into problems, be sure to check the Known Issues page which we'll update as necessary.