The issues might be caused by a few reasons.

First, make sure that your Internet connection is good and updates are not blocked because you’re on 4G/LTE and not on Wi-Fi. Second, make sure that your device has enough storage space to download the update.

Another thing is that the app is pending in the queue (the most common issue on Android devices).

Follow the steps below to clear the downloading queue:
  1. Open Play Store app.
  2. Swipe-in from the right edge of the screen, and select My apps & games.
  3. Here you’ll see all apps that are currently downloading on your phone. To cancel an app from downloading, select it and touch the X (cross icon) near the download progress bar to cancel download for the app.
    You can do this for all apps to clear the download queue.
  4. After that, please try to update the game again.