My 6s iPhone still cant update,why? I have give the space for 7,8 GB

Marking your own post as Solved may prevent others from trying to help because they think you have fixed your problem.

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

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 or later 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