First you need a new CPU as the one you have now is pretty aweful.
Like a AMD 1090T if you can find one, Or Phenom II X4 955 ~ 980 BE CPU.
Second as far as the graphics card is concerned you can put anything in the board you want. But if that system came with the stock power supply you are going to need something like this
To power something like this
Or two of these
I can't really recommend high end AMD cards right now due to Manfacturers charging over 100$ MSRP because people are buying AMD cards for Cypto Curriences (fake worthless money)
I5 3570K@4~5.0ghz: Gigabyte GA-Z77X-UD3H:Corsair Hydro H110 :16GB Corsair Vengeance DDR-3 1600: x2 XFX Radeon 7950 @ 1100/1575 : Corsair AX 860 PSU: x1 WD Black 1TB HDD's: 90GB Agility 3: 960GB SSD : Creative Labs X-FI:Corsair 500R Arctic White Edition:3 22inch Monitors Eyefinity @ 5294x 1050 : Alienware Tact-X Keyboard: Razer Naga :Corsair Vengence 1500 Headset: Corsair SP2500 Speakers