code: public static void removeRegistrationId(Context context) {
          final SharedPreferences prefs = getGcmPreferences(context);
          prefs.edit()
                  .remove(PROPERTY_REG_ID)
                  .remove(PROPERTY_APP_VERSION)
                  .apply();
      }
docs: Removes the current registration id effectively forcing the app to register again.
  @param context application's context.