HELP with choosing a COMPUTER

So I recently bought this for about 1000 bucks in Canada at Best Buy:
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c03...

Before I did research which was extremely stupid of me. I do understand that. So I planning on either upgrading it or replacing the whole thing and returning it if its still possible, I've used it already and obviously downloaded games,music and did other things but I don't think its been 30 days so do you think I would be able to return it?

If I was to upgrade it what card would you guys suggest for playing games like Battlefield 3 on max settings and Far Cry 3. Would I need to upgrade anything else? It came with a Radeon 5750 which is terrible but the CPU side looks really good with a i7 and 12 gb of ram.

I am a noob when it comes to stuff like this so I can't build my own computer but I think I would be able to replace a graphics card easily.

I've also considering purchasing this:
http://www.cyberpowerpc.com/saved/1ET0L9

Which seems much better. I made the build my self trying to keep under 1000 but it didn't work out but I'd still be willing to buy it if it would be able to handle Battlefield 3 and Far Cry on Ultra.

Any help would be greatly appreciated.