cannot update the latest version. Please help

Latest version of what? An IOS update?

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

iOS 14 and iPadOS 14 Compatible Devices

iOS 13 and iPadOS are compatible with these devices - Apple Support.    

iOS 12 is compatible with these devices.    

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