iOS 9 “Insufficient Space For Download” in Software Update
This pop-up error appears because your iPhone / iPad doesn’t have enough free space to download the new iOS 9 update.
Previously, in iOS 8, your iPhone / iPad should have at least 4 GB of free storage to install the update. This left users with 8 GB & 16 GB models frustrated.
In iOS 9, however, Apple has reduced the iOS 9 downloadable file from 4 GB to 1.4 GB. That’s almost 65% less.
So you need to have at least 1.4 GB of free space on your device before you could download the new update. And if you fail to have that much of space, the above error pops up.
Fortunately, as you can see from the screenshot, Apple has an option called “Allows app deletion” that will temporarily remove apps from your iPhones and iPads.
It creates the room required to download and install iOS 9 on your device. Once the installation goes smoothly, these deleted apps will be downloaded and restored from the App Store.