How can I update my iPhone 8 Plus?

beryl281 wrote:

I want to update this phone

Assuming you have a compatible device, see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support If the above Apple articles do not help, please post back with relevant information. 

iPhone 8 Plus cannot update to iOS 17 or iOS 18, if that is what you are really asking here.

If you want to run the latest iOS versions, it's going to be on a newer phone.