To issue an update, as far as I know, all you need to do is resubmit the app on iTunes Connect, ensuring that you have advanced the version number by 0.1 (for minor updates). Once it has been approved by Apple, it will replace the previous version of your app. Minor updates are free to existing users but new purchasers would be charged whatever price you set. There is a box to enter the "New in this version" text.