Hi intouchbable,
Welcome to the HP Community, I hope you enjoy your experience! To help you get the most out of the HP Forums I would like to direct your attention to the HP Forums Guide First Time Here? Learn How to Post and More.
I understand that you want to go back to Windows 7 after trying the 8.1 evaluation. You will have to use System Restore. Here is a link on using System Restore in Windows 8 it will be the same for 8.1. A System Restore point should be have been created when you upgraded. Let me know how it goes.
Thank you,
