It is important to keep the game updated because the latest versions have new functionalities, and also include bug fixes. Your player information and achievements are not lost when you update the game since they are associated to your email account. This being said, it is important to remember the account used to access the game and for it to be an active account.
You can update the game in the app Store found in your device. You can update the game by searching for it in the Store, where you will be given the option to update.