The game is designed to automatically detect your device and run with optimized settings. However, if the game is still not quite running as smoothly as you'd like, or if the battery is running down more quickly than you would like, you can manually lower the graphical settings. To do this, tap the cog icon from the Main Menu to open the Settings screen. From here, tap Graphics Settings.
To improve your game's performance or increase battery life, try reducing the Performance slider by moving it to the left. This will help the game run more smoothly and drain less battery by reducing the graphical quality of the game.