1. Launch the Play Market app on your device
2. Press the icon in the upper left corner of the screen, then select My apps and games
3. Find the game on the list and select it
4. On the game's page tap Update

You can also set up automatic updates:
1. Open the Play Market app
2. Press the icon in the upper left corner of the screen
3. Go to the Settings menu
4. Select Automatic Updates
5. Select one of the options:
- Always (apps will update through mobile networks and Wi-Fi)
- Wi-Fi only (apps will update only when Wi-Fi is available)