I Upgraded Windows 7 to Windows 8.1, Performance became horrible

Since i was using Windows 7 Home Premium, I can play games in high performance (i can ALMOST use the highest graphics)

Due to a problem that i posted here in SevenForums. I fixed it and upgraded my PC to Windows 8.1

But it seemed to look normal and fast (on other apps) but most of my games don't work, some were slow and laggy

What should i do? Is there anything to fix this? or should i downgrade it back to Windows 7?

THANKS FOR REPLYING!

The question is: Why did you upgraded from win 7 to win 8.1?
Win 10 is better than Win 8.x
Win 7 is better than Win 10

I had an old computer which originally came with Vista. It maxed out at 2 GB of RAM. I upgraded it to 7, then to 8 (each time doing a clean install). It ran well with both of these OSs. I then upgraded it from 8 to 8.1 by downloading and installing the free upgrade from Microsoft. When I got to 8.1, things got bumpy. It ran slower, and there were various issues.

One thing you could try: Run msconfig, and disable all non-Microsoft drivers. Then reboot. If your computer runs better, then re-enable the drivers you think you need, one at a time, rebooting after each one. When it slows down, then the last driver you enabled is the culprit. Disable that one, and continue re-enabling the rest, one at a time, till you see if there are any other culprits. Leave the culprits disabled, and things should be fine after that.

Try a different compatibility mode for the games. This is for Win 7 but should work for 8.1 also:

How to run older games on Windows 7 - Microsoft Community