I have downloaded a MKV video file (Blue Ray) but it runs too slow on my computer; is there anyway to fix it?

-Do you have a computer that supports HD? That may be your biggest problem if you don't. If you don't have a GPU and a monitor that can handle HD then it's going to be slow regardless of what you do.Some computers (especially those with some form of Intel graphics) just can't play HD video. If you've got a laptop, you're out of luck. If you've got a desktop, you can get a dedicated video card (any cheap one will do, as long as it's somewhat recent), pop it in, and be on your way.
Upgrade your GPU to CUDA enabled graphics card or you can convert your MKV video to SD video format by using BDlot Video Converter. And you can find the user guide here: http://www.bdlot.com/video-converter/
just uninstall that progeam, mayne ur computer doesnt support that