For iOS, you can delete the app by pressing and holding down on the app until it starts swinging left and right.
You should see an "X" in the top left corner. Tap that to delete the game and then reinstall from the App Store.
For Android, you can delete the game by tapping the device settings - apps - Air Combat - Clear cache - delete data - uninstall. But please don't do this if you haven't save the game progress to your Google account, because this action may result in game data lost.