While upgrading to iOS 8 OTA or via iTunes is simple enough, there are times when the ability to download the firmware for your device as a standalone file is helpful.
Whether you want to save bandwidth costs by downloading the file once and deploying to multiple devices, or if you have an unreliable Internet connection and you would like to be able to resume your downloads, you can directly download iOS 8 firmware files for your device. This also comes in handy when you want to restore the device at a later date.
If you are directly downloading iOS 8 firmware files, you likely know what you are doing, but here's a refresher nonetheless. Download the file corresponding to your device using the links below. Connect your device to a computer with the latest version of iTunes installed, launch iTunes, select the device and instead of clicking on Check for Update, press the Option (Alt) key on your Mac and then click Check for Update or if you are Windows, hold down Shift before doing the same.
Point iTunes to the file you've just downloaded, sit back and follow the iOS 8 upgrade instructions as usual.
Here are the iOS 8 direct download links: