Go to Storage Check under settings, then wipe to the right under details, wait for everything to load and then scroll down and click "clear" under Temporary files. That 500MB storage used up was probably used to storage the files required for the update, and now that you have updated, you no longer need them so it should be removed when you click clear. If it doesn't help, try this trick: change your date to the same date except one year later (2015), and then try the same clear storage thing, and then change the date back. Good luck!