Update your iPhone Using a Computer
Try Updating Using a Computer:
If you cannot update your iPhone from itself, then try using your computer (a Mac or a Windows PC, even).
How to do so: Follow these Steps...
1. Disable Cellular to Use the Computer:
Important: Consider disabling Cellular when updating the iPhone. Though it may not by necessary, it most certainly would save you lots of upfront money from data usage, as well as resulting in a reliable connection.
To disable Cellular on your iPhone, Go to: Settings > Tap: Cellular so that it its button is dulled out (grey in-color). You would end up updating using your computer, rather than cellular data.
2. Backup your iPhone: Be sure to back up your iPhone, that way you have something to restore your iPhone from, should anything go wrong with the update.
3. Update Using Links:
As a last resort:
- On the iPhone itself: Update your iPhone, iPad, or iPod Touch - Apple Support