Here download this benchmark program is very commonly used, then install it and if you are on 1080p, select that resolution or what resolution are you running, add a full screen checked, don't add MSAA- Anti Aliasing no need and try different setting low medium high or the very last extreme, but in most people run either the High or the very high. And the benchmark will start it will run different scenes of video material, in general, that's a GPU and CPU or whole PC configuration. And give us your final score when it finishes and min average and max fps, pay attention while the benchmark goes how are your fps stays.
https://benchmark.unigine.com/heaven
And as for clean driver uninstall here download Display Driver Uninstaller
https://www.wagnardsoft.com/
You will have to Run As Administrator and only in SAFE MODE.
1-
https://puu.sh/Bb9E8/41c7e652e9.png
2-
https://puu.sh/Bb9CS/31e5c17cec.png
3-
https://puu.sh/Bb9wZ/4607380b9e.png
So download DDU extract it, then click on it and it will open as in image 1 then go up in the corner and click options
as you see in image 2 make all boxes checked or unchecked as it is same then close it, and then run it again
and it will be as in the image 3, click on Safe Mode Recommended and PC will restart in SAFE MODE, when you will be in safe mode Run the Clean and Restart - the Recommended one and it will start to clean your drivers and will restart PC, then you will be fully clean from any previous drivers and then you can re-install your drivers again from the AMD page.
If there is something that you don't understand write me!
From here download your AMD drivers again for the clean installation
https://support.amd.com/en-us/download