Problems with updating iphone
Scroll through it until you see Software Update, then select this entry and tap Delete Update. In my experience, these four steps will fix any problems with regular Apple updates and will let you upgrade your device to the latest version of i OS.
If you want to try out the latest releases before anyone else, you have to sign up for the Apple Public Beta service on each device you want to use.
Once you've done that: here's how to fix the annoying "Unable to Verify Update" i OS error for i OS 11, i OS 10, i OS 9.3 and below.
Regular updates are the official versions that Apple releases to the public, having completed its testing on all devices.
Once complete, rejoin the beta programme following the link above, reinstall the beta profile and then you can re-run Software Update and get the latest beta version of i OS.
It's also important that you're connected to a home network, as many company networks might filter out the connection to Apple's servers.
Be warned, doing this will require you to enter all of your Wi-Fi passwords again.