iOS 8 is Apple's most recent major revision of the software for your iPhone and iPad. If you haven't updated your device to iOS 8 because you've been getting an error that there is not enough storage, here’s a useful tip.
Connect your iPhone/iPad to a computer. If the latest version of iTunes is installed, you’ll get a notice indicating that there is a software update for your device. iTunes will download the update on the computer and then install it on your device.
Future updates will be smaller in size; you won’t need to connect to iTunes for every update.