If you are trying to download the iOS 8, probably you're also complaining about the huge download file size. You will need to free up 5.7 GB of your storage in order to complete the download. As a result, people started backing up and deleting photos, music, videos and other files just to make room for this download file. Before you waste your time and effort doing this, there's a way to download it without deleting everything.
How to Download 5.7GB iOS 8 Without Deleting Anything?
1. Plug your iPhone or iPad to the computer
2. iTunes will detect your device. Make sure that the latest version of iTunes is installed.
3. Click "Check for Update" button (not the Restore iPhone)
4. Download and install
|Photo Source: Mashable|
Take note that iOS 8 is compatible with iPhone 4s, iPhone 5, iPhone 5s, iPhone 5s, iPhone 6, iPhone 6 Plus, iPad 2, iPad 3rd generation, iPad 4th generation, iPad Air, iPad mini, iPad mini with Retna Display, iPod touch 5th generation.