iOS 9 Download
When the iOS 9 update becomes available, you'll be able to download it Over-the-Air or through iTunes. That said, the iOS 9 download is going to be a little bit different.
While iOS 8 required 4.6GB of free space to install, the iOS 9 update should only require about 1.3GB of free space on your iPhone, iPad or iPod touch. This should be music to the ears of those with a 8GB or 16GB device.