If you cannot update after the game redirects you to the App Store (update is unavailable), please follow these steps and you should be able to update:
- Close the game by double tapping the home button and closing the game by swiping it up
- Open the App Store and go to the Updates tab
- Swipe down to refresh the list. You should now see the Update button next to Empires & Puzzles app. Tap the button to update your game.