The Android build system uses the Android Plugin for Gradle to support building Android applications with the Gradle build toolkit. The plugin runs independent of Android Studio so the plugin and the Gradle build system can be updated independently of Android Studio.
Use gradle wrapper (recommended) - select this option to use Gradle wrapper. Using Gradle wrapper lets you get automatic Gradle download for the build. It also lets you build with the precise Gradle version.
Newer versions of the Gradle plugin may require newer versions of Studio to enable the new features in the IDE, but the project should open in older versions of Studio, and build from there (since Gradle does the build). We will be very careful about this.
Click on Settings -> Build -> Execution -> Deployment ->
Gradle -> Select default gradle wrapper
You can use
classpath 'com.android.tools.build:gradle:2.0.0-alpha3' // or alpha2
Or //classpath 'com.android.tools.build:gradle:2.1.3'