What kind of system (manufacturer/model) or motherboard (same info)?
Is this onboard video or an actual physical card that is installed?
If it's onboard, all you have to do is enter the BIOS and disable the onboard.
If it's an actual video card, then you need to remove it via Device Manager (remove the drivers) and then open the case and physically insert the proper card into the proper slot.
Note: You need to make sure that your motherboard can accommodate the card that you determine you want to install. One size does not fit all...in fact some motherboards may not have a slot for an actual physical card.
If you all ready think you know or have the card...tell us the manufacturer/model and someone can tell you if it will work in the system you intend to put it in.
How to get into your computer's BIOS - http://www.cyberwalker.net/faqs/reinstall-...enter-BIOS.html
Device Manager Basics - http://www.cybertechhelp.com/tutorial/arti...-manager-basics http://www.motherboards.org/articles/guides/1168_1.html