Q: My iphone 6 downloaded iOS 10 and will not install it

You can try going to Settings>General>Storage & iCloud Usage>Storage>Manage Storage. Find the iOS update, and delete it. Then go back to Settings>General>Software Update. Make sure the device is connected to wi-fi and power. If that does not work, then connect the device to the computer and iTunes and update from there.

I think that Chris has given you very solid advice, but before you delete the download and start all over again, try restarting your phone. It is easy to do and it might jump start the process. It might not do anything at all, but it's worth a try before you start all over again.

So you are saying that you have done everything the two of us have suggested? It is while connected to the computer and iTunes and it will not verify? What other message appears on the screen? Also, telling us that in the beginning would have prevented us from wasting your time with recommendations that you had already done.

Go ahead and look at this support document for assistance. If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support

Run the update connected to itunes. Make sure you have the latest iTunes downloaded though.

As the poster before you has stated, make sure you have the latest version of iTunes, 12.5.1, and follow the steps in the link I provided you.

Have you tried using another WiFi network? Power cycle your router? Tried a force restart of your device? .....press and hold both the Sleep/Wake and Home buttons for at least ten seconds, until you see the Apple logo.