How can I update iPhone 8 to iOS 15?

You can't, you can only update an iPhone 8 to 16.7.10

• 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 15.8.3

• If you have an iPhone 8 or X, you can update to 16.7.10

• If you have an iPhone SE (2nd generation or later), or XR through 16, you can update to 18.3

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

No, it says it must be iOS 15 or higher. If you are on the latest version of iOS for you model phone which is 16.7.10, YouTube will work on your phone.

Cutsie Dan right for one thing he had a iPhone 7

I have no idea what that is supposed to mean.

iOS 15 would be a minimum requirement for youtube, but it will run on iOS 16, 17 and 18.

As we mentioned in our first reply, your iPhone 8 will update to iOS 16. This is a good thing, since iOS 16 is more advanced than iOS 15. Lucky you.

iPhone 8 would update to iOS 16.

Make sure that the phone is fully charged and has a good strong Internet connection.

Settings > General > Software Update

What part of you can only update an iPhone 8 to 16.7.10 did you not understand?