video card upgrade. i need help 537s Q8200 quad 4 gb ram 1.32 tera bites of hd

i have a 537s q8200 quad core 4gig ram 320 gig hd and the current video card is 3450 ati radeon . its not enough. power supply is 250 and i think i have 22 point which is labaled as p1 and a 5 wire connect that is labeled p3 comming from power supply to motherboard. have external terabite hd also . i have 1 pci express x 16 and 2 pci card spots . what can i do to make this pc its best for gamming at reasonable cost. plz help and those 2 pci slots are unused what can i do with them. when i check and see if i can run it .com to see what games i can run , usually cannot because of video card not enough . i guess it says 256 mb instead of 512 for the card . i need updated accurate info on best video card upgrade i can do with theses specs from my model pc. have reasearched many things . still dont know what to do. thanks .also not sure what 6 points or more on psu meams. i need that im told .