I don't see much of a problem here. Your rig looks like it's performing more or less on target. Consider lowering the visual settings if you want to get a higher FPS.
However I'll do my best to give you a few options and some info:
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Your CPU is alright.
Your RAM is alright. You could go up to 8GB, but to take advantage of that you'd need a 64-bit version of Windows, and it's less pressing than some other upgrades.
I think your graphics card is the thing you could do with upgrading most. Basically, the larger your screen, the more powerful graphics card(s) you need to get high FPS and maintain higher settings. Because your screen is quite small, you don't need to splash out
too much. However this does mean that if you ever upgraded your screen to a larger size (which equates to a higher resolution) your FPS would go down, and you'd probably have to lower your settings considerably to maintain decent FPS.
So you have two options:
1 -
If you plan to stay with your current monitor for the forseeable future, get a mid-level card, as much more would be a waste of money. I don't suggest you get anything more expensive than a GTX 560.
2 -
If you were planning, or want to upgrade your monitor, get a slightly more expensive graphics card so that not only will it handle well on your current monitor, but it also will be ready for the demands of a higher resolution monitor as and when you get it. Get the best you can afford.
Use this article to compare graphics cards and decide which'll be best for you by comparison:
http://www.tomshardware.co.uk/best-graphics-card,review-32225.html
Remember to consider that a more powerful card generates more heat inside your system.
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If you're not willing to buy a new graphics card, then all I can suggest you do is:
Check all your drivers are up to date.
Run malware, virus and spyware scans.
Defragment your drives.
Lower your visual settings in games.
But to be honest, your rig looks to be performing more or less as it should.
Just a final thought:
If you're running on stock cooling, don't even think about trying to overclock to increase your performance. You'll almost certainly damage your PC, possibly permanently.
If your rig is bought from a company, remember to check when your warranty ends. If you're still covered by warranty, ask permission before you change any hardware in your rig, as their coverage is a safety net that not only did you pay for, but is also usually very useful if things go awry. If not, go ahead and change what you like, but don't expect them to help you much/at all if anything goes wrong.
If you want to buy new components, try to steer clear of sites like Ebay, as there is a total mix of quality items on there, with some true bargains, but also some utter crap that will be a total waste of money, if if faulty could be negative addition to your computer. Buy from reputable website such as www.scan.co.uk or www.overclockers.co.uk - both of these companies are the ideal place to buy PC stuff from, even if they are a bit more expensive than Ebay.
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Hope that helps a bit,
Best of luck,
-Nih