How to get iOS 8 without deleting everything on your phone
If you’ve tried downloading iOS 8, or know anyone who has already done so, you’re probably familiar with the biggest complaint: The download is huge.
It’s not that iOS 8 occupies a ton of storage on your iPhone or iPad (iTunes says the file is about 1.2GB), but rather that the download itself needs up to 5.7GB of free storage to be completed.
As a result, people are scrambling to delete pictures, apps and music in order to make room for iOS. The previous version, iOS 7, only required 2.9GB of space to install, so the added storage requirement has hit some users pretty hard. Note: Depending on which model you have — and the last time you updated the iOS — how much space you’ll need in order to download the software will vary.
Sources from http://www.smh.com.au/