How do I change the video card in my computer?

I bought a Dell Dimension 4400 (used from work) I think I have to change the video card because the colors are terrible... when I go to Display Properties for the color options I only have 16 Colors and Screen area can only be 800 by 600 pixels... can I change the video card? how much it is? can I do it myself?How do I change the video card in my computer?
I think almost all of AGP 4X can work on your PC. If the Color can only be 16 color and 800x600px, maybe you should check the driver. try to download it from web. For example :

For ATI RADEON / Other SERIES, try to download a new one from http://www.ati.com

For NVIDIA GeForce / Other SERIES, try to download a new one from http://www.Nvidia.com



to check your VGA type, Click right on ';My Computer';, choose ';Properties';, go to tab ';Hardware';, click ';Device Manager'; and expand the ';display adapter'; tree. There you can find what's the type of your Graphic Card.How do I change the video card in my computer?
First I would go to the the video card manufactor and look for an updated driver. That may be all you need to do