I want to update my iPhone

Here's two different ways to ensure the highest iOS that your device will support is on your device.

Update your iPhone, iPad, or iPod touch wirelessly. Click here --> Update your iPhone or iPad - Apple Support

Update your iPhone, iPad, or iPod touch with the Finder on a Mac computer --> Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

Your iPhone 6s can only update as far as iOS 15.7.2

Appears that there is now an iOS 15.7.3 version.

Thanks Bob Timmons.