The now removed updater has made the same:
Downloaded the RetroArch.7z to a temporary folder and then extractet it in your current folder with overwriting existing files.
System files. No config overwriting.
You can check the content of the *7z before extracting.
But since a lot of menu entries have changed from 1.9.0 to 1.9.7 i suggest you extract it to a new location and check the new features to become familiar with them.
For every feature added (or removed/changed) you should maybe check the release logs: https://github.com/libretro/RetroArch/blob/master/CHANGES.md