Hi I cant update My iphon

Go to Settings > General > About

What does it say for iPhone Model?

You need an iPhone 6s/6s Plus or newer in order to run iOS 14

Supported iPhone models - Apple Support

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

issues?

Updating iOS: common issues and solutions - Apple Community

video..

Which phone? What is your current iOS version? Any error message? Trying over WiFi or through your computer?