Open the settings, and look for the entry labeled "Auto-update apps." Tap on it, and you'll have the choice to update apps over Wifi only, update apps over any connection (this might use lots of data) or to turn off automatic updates. Apps that require new permissions won't just automatically update themselves without your approval.
Be sure to have the "Notifications" box checked, and when an app you have installed needs new permissions to update, you'll get a notification about it in your status bar.
Under the General headline, just simply put a tick on the box next to the lines: "Auto - update apps".
Make sure everything is in your control one last time, and then you will see the difference.
Maybe you want to read change logs, or want to read what others are saying about the latest version before you jump in and update.