You just intall it make sure all the cables are hooked up right and I think you have to connect a 6 pin connecter to the back side of the card. I don't know much about the HD cards. Then make sure your cable is from the monitor to where your card is not where your on borard was.
Then boot up and when it is booted then make sure all drivers for it is up to date but you can do that at any time you want. Later if you want to disable the on board graphic then you can do it from device manager or your bios.
It is not nessary to do it at all if you don't want to, I hope this was a little help and Good luck to you