You need to be sure if your system can be upgraded first of all. This means a couple of things, primarily if your case can fit a new video card. Next, you need to know what type of power supply unit you have, and what it's rated for, and what connectors it has. Almost all new cards will need to connect to your PSU, at least anything decent.
Your current card won't see much improvement overclocking, if that's what you were asking, at least IMO.
You can have an i7 cpu, but a crappy motherboard and PSU which will make it nearly impossible to upgrade your video card, so you need to check into that before any purchase. I have a home theater PC that is an HP, and it's an i7 920, with a 5770 video card, and the only card I could get into it with the current MB and PSU was a 7770, which wasn't really worth the small increase in performance. I suspect your box will be similar in terms of the situation. Maybe take a look at your make and model and post it, and others here can help you out a bit more with that info.