how to update iphone 6 to 14 from 13

pjbonds wrote:

But I can’t seem to do it from my computer. Can you advise?

General info: Learn how to update your device manually if you're using a Mac with macOS Catalina or later, or if you're using a Mac with macOS Mojave or earlier or a Windows PC.

Then this article: If your computer doesn't recognize your iPhone, iPad, or iPod - Apple Support

Is there a reason you want to do it from your computer rather than over the air?

Do you have a beta version on the phone (go to Settings/General/Software Update, and if it shows any version other than 15.6.1 that is the problem)? If you do, see→How to uninstall iOS beta software - Apple Support

If you want to use your computer, see→Update your iPhone, iPad, or iPod touch - Apple Support

If you have Windows it must have the latest version of iTunes, from https://itunes.com

You can’t update to iOS 14, but you can update it to iOS 15.6.1. Go to Settings/General/Software Update and follow the instructions.

To update over the air from the phone all of these requirements must be met:

• You need at least 6 GB of free storage
• You must be connected to a Wi-Fi network (and not a personal hotspot)
• The phone must be charged to at least 50%, and preferably plugged in so it stays above 50% during the update
• The phone must not be in Low Power Mode
• The phone must not be connected through VPN, and it may be necessary to delete any VPN apps and VPN profiles
• The phone cannot be in Airplane mode
• You cannot still have a beta version installed on the phone
• You cannot have a previous version that was downloaded, but not installed - go to Settings/General/iPhone Storage to look; if you find an iOS installer, delete it

If you can't meet all of them you can still update using your computer.

If your phone is running iOS 13, it can not be an iPhone 6. Any update will be to the most recent, compatible version, in this case iOS 15.6.1.