why I cannot update ios via cellular data?

Apple limits the amount of data that can be downloaded over cellular in an app update.

An iOS upgrade might be more than some people's monthly limit for data.

Find a Wi-Fi network, or hook up to your computer with iTunes (if you have one).

No, Wifi providers don't distribute iOS updates either. The only distributor of Apple updates is Apple. You need to be connected to Wifi in order to download the update over air.

When you connect your iPhone to your computer with iTunes open, a small phone icon will appear in the upper left side of your screen (it takes a couple minutes for it to appear). Once it does, click on the icon and that's what opens your phone to iTunes to let you choose the iOS update.

Hi.

As far as I know - and I may be wrong - but cellular companies take a long time to start distributing OS updates through their own data systems. If they don't decide to distribute the OS updates, you can't get OS updates.

In such a case, your only options are wi-fi or iTunes with a computer. If you don't have any of these options, you must contact your cellular contractor.

You can connect your iPhone via USB cable to your computer and update it via iTunes. You'll need iTunes v12.7. This and having wifi are the only two possible ways. If you have an Apple Store near you, you could take it there and Apple may be able to update for you.

Cellular providers do not distribute Apple iDevice updates.

Does WiFi providers meant to do?

This is not the reason.

Thank you for correcting me. As I wrote " I may be wrong ". Apparently, I was wrong.

Hi also have this problem but from taking the advice by connecting to itunes 12.7.1 there is no option of "summary" Apple please explain?