If you don't have enough space on your iPhone , you may not be able to install new updates on your iPhone. Go to software update and you may be promoted with a window saying you don't have enough space to perform this update. This happen frequently with 8Gb and on even 16Gb device.
To update your iPhone without deleting anything on your iPhone to create massive 5gb space for update, just connect your iPhone to Pc or Mac. Make sure you have iTunes installed on your Pc or Mac. Select your device and click on check for update. iTunes will download and will install the update on your device without requiring large space on your iPhone.
So next time you install new update, make sure you use this strategy to avoid storage error.