yup, guess i did.
mobo make n model will tell what your options are for keeping it and upgrading the other bits...
tomshardware has a budget pc build every few months.
as of two months ago this is their 500 $ build
CPU AMD Athlon X4 860K
Graphics Gigabyte GeForce GTX 960 2GB
Memory Corsair Vengeance 8GB (2x 4GB)
Motherboard Gigabyte GA-F2A78M-D3H
technically, thats a build submission from a reader...
they built
Q1 2016 Low-Budget PC Component List
Processor Intel i3-6100 (Skylake) $129.99
CPU Cooler DeepCool T200 $14.99
Motherboard ASRock Z170 Pro4S $79.99
Graphics Asus Stric GeForce GTX 950 2GB $155.09
Memory Mushkin Redline DDR4-2400 CAS13 (2 x 4GB) $42.99
System Drive WD Blue 1TB 3.5" $53.99
Power Antec VP-450 $37.99
Core Cost $515.03
Case Rosewill Redbone U3 $42.99
Total Performance Cost $558.02
Storage Drive None $0
Optical Drive None $0
Total Hardware Cost $558.02
OS Windows 10 x64 Home $104.48
Complete System Price $662.50
my boys pc, i bought from walmart in 2012, we upgraded ram, video card and hard drive since then.
Intel Core i5-2500K Processor,
8GB Memory,
1TB Hard Drive
and Windows 7 Home Premium
GeForce GT 520 Graphics
added
SAPPHIRE Radeon HD 7870 GHz Edition OC 2GB
G.SKILL Ripjaws X Series 16GB (2 x 8GB) DDR3
here is hierarchy chart for comparison of video cards.