cyberjunaid

open your case and measure your usable space from the inside. Don't just rely on the external dimensions. You'll have drive cages and wires to contend with on the inside. any card you get is going to be at least dual slot (stay away from triple slot. it's a waist of space in your case.) so make sure your case has enough PCI brackets on the back. From the pictures I found it looks like you should be fine.
 
In terms of the card, most manufacturers list the card length. try to leave yourself a little room though. If, for instance, you only have 12 inches of usable space in your case then don't get a 12 inch card if you can avoid it. you could run into clearance issues. Leave yourself an inch or two of wiggle room.
 
Remember you'll need space to run power as well. Depending on the card you get you may need anywhere from a single 6 pin to dual 8 pin. it's probably not going to be a problem, just something to keep in mind.
 
So chose the card you want, measure the inside of your case, get a version of that card that leaves you some wiggle room and get a power supply that can handle it.
 
If you need anymore help feel free to PM me.

yes, why wouldn't you be able to? you could get a 1080 or a Titian if you had the money. nothing is stopping you from putting any graphics card you want in that computer. just make sure you get a power supply big enough to handle it. A 650 Watt PSU will push almost any card you want. just make sure it's single rail.
 
I'm running the same CPU you are and I have dual 970s. You might be a little bottle necked but that's unavoidable unless you just build a whole new PC. Buy the best card you can afford and that thing will be a great little computer. Just carry the card over into your next PC when you upgrade.

I was thinking about Antec VP-450 power supply I recommended to you earlier and realized it was a terrible recommendation... If you do pick up a new Power Supply read the description carefully and make sure It's a "single rail" power supply. Without going into to much technical detail it basically means the PSU can deliver it's full load where you need it to go. I'm currently being screwed over by a dual rail PSU and I accidentally recommended one to you too.
 
Get something somewhere in the vicinity of 500 or 600 watts. Any more than that and you're wasting both power and money on that computer. 600 Watts would run a GTX 1080 so it'll be more than enough for any lower level cards.
 
And make sure to get a good brand. Corsair, EVGA, Seasonic and Silverstone should all be fine. Stay away from Thermaltake, Rosewill and any off brand units unless you want a dead PSU, a dead computer or a house fire.