Why the button for allowing download is not blue

Phone will not update

Check all of these carefully:-

·       you are on a good Wi-Fi, (from 15.4 iPhone 7 up, you may be offered cellular update)

·       Plenty of spare storage – 6GB at least.

·       on charge with more than 20%, OR 

·       off charge with more than 50%

·       low power mode turned off. 

·       Check Settings, General to make sure you have no Beta profile installed.

·       no VPN installed (Check Settings, General, VPN & Device Management)

Resources:-

Update iphone

Update your iPhone, iPad, or iPod touch - Apple Support

Learn how to update your iPhone via recent Macs here:-->

Update your iPhone, iPad or iPod touch with the Finder – Apple Support (UK)

or older Macs and PC here:-->

Update your iPhone, iPad or iPod touch with iTunes – Apple Support (UK)

KB Article - Iphone will not update

If your iPhone, iPad, or iPod touch won't update - Apple Support

I just gave you all the help there is from here. If you need more help you hould reach out to Apple Support directly. You should be able to reach them here

Contact - Official Apple Support

or phone numbers

Contact Apple for support and service - Apple Support