How to recover the previous 6.0 android version after upgrade to 7.0


AC Question

The new version 7.0 was automatically installed on my Galaxy S7. After a few days I'm v convinced at all that was a mistake. I have several reasons6 to think so, like crashes in programs that was ok, unintelligible notification screen, confuse little icons that were ok before, etc..
Please help me to restore the previous 6.0 version.
Thank you