ngintel77 :
If your computer come installed with DDR3 Ram (8GB) can you replace that with (8GB) of DDR5 Ram
You are confusing video RAM with system RAM. Unless or some reason you think DDR5 is available for regular RAM slots.
If you are actually looking for a video card, the type of RAM is uses does not matter, you can use a GDDR5 video card in a syste with DDR3 RAM, or DDR2 for that matter.