Where are iOS updates in El Capitan located on Mac

The file should be in ~/Library/iTunes/iPhone Software Updates not /Library/iTunes/iPhone Software Updates

The first is your personal User Library, the second is the System Library.
The tilde ~ sign is an abbreviation recognised by the System meaning Boot Drive/Users/Your Name/ & saves having to know the names of the boot drive & current user.
It's kind of the Mac equivalent of using %appdata% in Windows to find the current user's Roaming folder - an environment variable.

By default ~/Library is hidden, so delving down the file hierarchy manually you won't find it.

You can get to ~/Library from the Finder > Go menu if you hold Opt ⌥ whilst selecting the folder, but if you have a specific destination, I find it easier to Go directly there…

  • In Finder, Cmd ⌘ N for New window
  • Cmd ⌘ Shift ⇧ G for Go…
  • Copy/paste ~/Library/iTunes/iPhone Software Updates including the tilde ~ & hit Enter ⌅