I want to update my iPhone 8

Update your iPhone, iPad, or iPod touch

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.7

• If you have an iPhone 6S through 7, or SE 1st generation, you can update to 15.7.9

• If you have an iPhone 8 or X, you can update to 16.7.1

• If you have an iPhone SE (2nd generation or later), or XR through 15, you can update to 17.0.3

Go to Settings > General > Software Update.

This link will show you how to update your iPhone, iPad, or iPod touch using WiFi -

Update your iPhone or iPad - Apple Support

This link will show you how to update using your computer -

Update iOS on iPhone - Apple Support

supakorn77 Said:

"iphone8 update software: I want to download software for iphone8 new version. My software is version 14.7.1 I want to update software version. What can I must to do?"

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Successfully Updating an iPhone...

Update Using a Computer and Ethernet:

Alternatively, you can use Ethernet through a computer.... To avoid this persistent notification on your iPhone, try updating via a computer. If you cannot use Wi-Fi, then use Ethernet.  Go Here: Update your iPhone Using a Computer - User Tip

As for Ethernet:

On the computer, you would connect it through Ethernet, going directly into your router. For a Mac (or PC) that does not have Ethernet, this would be the adapter to use: Belkin USB-C to Gigabit Ethernet Adapter - Apple