I can’t update my iOS version

https://support.apple.com/en-ie/HT201263

Put your device in recovery mode and set it up again

1. Make sure that your Mac is up to date. If you're using iTunes, make sure you have the latest version of iTunes. 
2. On a Mac with macOS Catalina, open Finder. On a Mac with macOS Mojave or earlier, or on a PC, open iTunes. If iTunes is already open, close it, then open it again. Find out which macOS your Mac is using.

Sorry, but with so little information we cannot give any definite advice. What are you seeing when you try to update? What iPhone do you have? What version is it on now?

And btw, this is not a support chat site; it’s an online community of users. You do have to wait for a reply sometimes.