How do I find the right graphics card for my computer?

[sheratchet]

What is it I have to look at when buying a new graphics card? I bought a hp desktop 1 year and a half ago and I want to upgrade the graphics card but dont know how. How do I know if the graphics card will fit in my computer and if it will be able to read it. Sorry Im a bit new at this so I would appreciate any kind of help.

 

[iceclock]

What's ur model number and budget

 

[sheratchet]

What's ur model number and budget

The model is p7-1247c. Budget $150

 

[iceclock]

U need new powersupply. Xfx 550 watt powersupply plus Radeon 7700