The game is designed to automatically detect your device and run with the best settings. However, if the game is still not quite running as smoothly as you'd like, you can manually lower the graphical settings. To do this, go to the settings menu by tapping the cog at the top right corner of the Title Screen, then select the Graphics Quality option.
The Graphics Quality sider will change the quality of some effects and visuals, while the Resolution Scale slider will affect performance by increasing or reducing the overall sharpness of the game.