I want to update iOS 14 in my iPhone

Go to Settings > General > About

What does it say for iPhone Model and Software Version?

No iPhone model can be updated to iOS 14.

If your iPhone is an iPhone 6/6 Plus or older, then you cannot upgrade beyond iOS 12

You need an iPhone 6s/6s Plus or newer in order to run iOS 15..

You need an iPhone 8/8 Plus or newer in order to run iOS 16..

Supported iPhone models - Apple Support

If you are running into an app that is not supported for your iOS version.. then you'll need a newer model iPhone in order to run that app.

Otherwise, if just needing general info about updating:

have you read thru this support article for updating?

Update your iPhone, iPad, or iPod touch - Apple Support

need more storage for update?

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

issues?

Updating iOS: common issues and solutions - Apple Community

video..