I need to do the software update but it will not let me do the software update

What happens when you try? Error message(s)?

Is your device compatible to update to the new version? See the Apple Support article(s) below. 

iOS 14 and iPadOS 14 Compatible Devices

See the articles below.

Update your iOS device.        

Get help with over-the-air iOS updates          

Update – Can’t or can’t restore 

Have you tried using iTunes on a computer or Finder if running Catalina to do the update?

 Update software on iOS devices in iTunes on Mac

If you see an error when you update or restore your iPhone, iPad, or iPod      

Updating iOS: common issues and solutions