And back again
As we mentioned, Apple traditionally stops signing old versions of iOS just a day or two after releasing major updates (such as iOS 8). If you were to update to iOS 8 say, a week after it ships, you might find that you can't go back to iOS 7. So, if you intend to be among the earliest adopters, it's not a bad idea to have a copy of the iOS 7.1.2.ipsw file at hand.
If you have a copy on your hard drive you will find it, by default, by following this path: youruserfolder/Library/iTunes/ and then within a folder called iPad Software Updates, iPhone Software Updates, or iPad Software Updates, depending on the devices you use. (You access the Library folder in your user folder by holding down the Option key in the Finder and choosing Go > Library.)
The Mac will delete these files under certain circumstances so you may not have a copy of the latest one. If you don't, launch your favorite Web browser and search for download ipsw. You'll find a number of sites that offer links to the file you need. Just be sure to choose the correct one based on the device you're using.
If you revert before Apple stops signing iOS 7, the trip back shouldn't be too painful. Just jack your device into your computer, launch iTunes, select your device, click the Summary tab, and while holding down the Option key, click on the Restore button. (If you've enabled the Find My feature you'll need to disable it on the device first.)
Do so and a navigation window will appear. Use it to locate the iOS 7.1.2.ipsw file and click Open. If things go according to plan, the Mac will set about installing iOS 7 on your device. When it does, it will wipe out all the non-stock apps and data on it, so be sure to make a backup before you begin.
If you're instead told that you're already running the latest version of iOS on your device (and you know that iOS 7 is still signed and allowed), you may have to put your device into Recovery mode. You do this by shutting down your device, plugging the syncing cable into your computer, and then holding down the Home button while you connect the syncing cable to it. When the Connect to iTunes screen appears, release the Home button.
iTunes will report that your device is in Recovery mode. You should now be able to hold down the Option key, click the Restore button, navigate to the iOS 7.1.2.ipsw file, and install it on your device. Should you see an alert that this version of iOS is not compatible with your iPhone, iPad, or iPod touch, it means Apple has stopped signing it and you must run iOS 8.
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