my iphone cant update to new ios！？

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

Your phone might need to be on a charger to update.

Why not? What happens when you try to update exactly? Any error messages? If so what do they say?