Summarize the following:
It's the blue circle with the white A inside. Tap the icon to open the App Store. Scroll through Pending Updates to see if Minecraft: Pocket Edition is listed. If there's an update available, it will show up under that list; if you already have the most current version, Minecraft: Pocket Edition will not be listed. Minecraft: Pocket Edition will begin to update automatically. For iOS 7 and later, you can set up automatic updating for apps. To do this, go to Settings > iTunes and App Store. Under Automatic Downloads, turn on automatic downloads for updates (so that the button is green). Turn off "Use Cellular Data" if you only want automatic downloads to occur when you are connected to Wi-Fi.
Open the App Store on your Apple device. Select the Updates from the bottom tabs. Tap Update.