I am unable to do update and I have space also
I am unable to update and I have sufficient storge.
iPhone 6s Plus, iOS 11
Question marked as
Your products list (at the bottom of your question) shows that you have an iPhone 6s Plus, running iOS 11.
Should be this case, iOS 11 is a very old operating system version and you won't be able to update the device to the latest iOS (now 15.3) wirelessly.
I suggest that you update it via computer (if you don't have a computer borrow one from your friends/neighbors/relatives, or ask for help at an Apple Store or Authorized Service Provider), then learn how to update your device manually if you're using a Mac with macOS Catalina or later, or if you're using a Mac with macOS Mojave or earlier or a Windows PC.
If you still get no help, contact Apple Support directly, using this link:--> Get Support
Regards
Giulio