How can I update iOS on my iPhone 8 Plus?

You can update an iPhone 8 Plus to the latest release of iOS 16.

About iOS 16 Updates - Apple Support

Update your iPhone or iPad - Apple Support

Updating iOS: common issues and solutions - Apple Community

You cannot update an iPhone 8 Plus to iOS 17 or higher. For the iPhone 8 Plus, which originally ran iOS 11, iOS 16 is the end of the line.

An iPhone 8 plus can be updated to iOS 16.7.11, no further -

• 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 15.8.4

• If you have an iPhone 8 or X, you can update to 16.7.11

• If you have an iPhone SE (2nd generation or later), or XR through 16, you can update to 18.45

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