Updates: how to turn on and off

Since the introduction of the App Store, Apple has made automatic updates of iOS on the iPad, iPhone, iPod Touch, and Mac OS on Macs happen by default. Understand, updates are there to provide security enhancements for your system, and compatibility for newer features. On iPads, iPhones, and iPod Touch, the Settings App -> App Store selection lets you change the update automatic settings from on to off. On Macs, Apple menu -> System Preferences -> App Store lets you do the same.

Before any update you should backup your data. You should also verify the space requirements are met by your device, and that you need the features of the update. Frequently there is no way to turn back the clock. iOS devices made that especially hard as my tip:

https://discussions.apple.com/docs/DOC-8871

explains.

Be mindful, it is a good idea to have a stable secure WiFi or ethernet connection before downloading any installing any updates, as open WiFIs frequently have wildly fluctuating connection speeds, and cellular connections drop easily. If you can't establish a secure WPA2 WiFi or ethernet connection directly to the internet, wait until such time you can. Users, including the author of the tip, have inadvertently selected update now on the screen because the update notification was partially present on a small iPhone screen, and not obviously there. Because of issues mentioned on tip 8871 above with synchronization issues with older Mac OS systems, you need to be especially vigilant to only update when you are prepared.

https://discussions.apple.com/docs/DOC-1992

Additional information will be added in the future.