How can I update to iOS 14

You can’t; iOS 14 has been discontinued.

Go to Settings/General/About and note the iPhone Model Name, then check its version compatibility from this list:

• iPhone 8 or newer, including SE 2nd and 3rd editions, you can update to 16.6
• Any iPhone series 6S and 7, and original SE: You can update to 15.7.8
• iPhone 5S or 6: You cannot update to iOS 13 or higher; you can update only to iOS 12.5.7
• iPhone 5: You can update only to 10.3.4
• iPhone 5C: You can update only to 10.3.3
• iPhone 4S: You can update only to 9.3.6
• iPhone 4: You can update only to 7.1.2

If your phone is eligible to be updated go to Settings/General/Software Update and follow the instructions.

You cannot. iOS 14 is no longer available to update to for any device.

If your device supports iOS 14, it also support at least iOS 15 or even iOS 16 and only those are available to update to now.

If you have a device that supports the update, then follow the steps in the support document you posted from.

What device are you trying to update exactly?

For iOS 15 you need an iPhone 6s or iPhone 7.

For iOS 16 you need an iPhone 8 or later.

You can't update to iOS 14 because it is no longer available.

What model of iPhone do you have? Not sure?

Settings > General > About > Model Name