Updating An App While Retaining Players Highscores,Unlockables Etc.

Hi guys, at the momment I am in process of trying to store the players scores, unlockables etc in a file on the device. However when I was thinking about it a little more I was wondering if I were to say update my app and the user re-downloaded the the updated app, wouldnt this delete all of their scores and critical information when they did this? And if this is so, how would I go about updating an App while retaining the players scores etc and bringing them over to the new updated app?
Thanks in advance.