Just done a quick search on utube for this game http://www.youtube.com/watch?v=v5pB6j9rYzY looking at it, It seems to be flash based game so there is no real reason your GPU should feeling the workload. In saying that AMD 4800 is the series but not the card if its a 4850 then it's a budget card or the 4870 is a good card a few years ago.
So pop the side of you case open turn of the power and buy your self a Air Duster (compressed air) and blast that sucker clean! keep the can upright or it can blast cold liquid if upside down. make sure to clean the fans and keep the straw about 3/4 inchies from the board / fans.
i would also recomemd a quick MSCONFIG of your machine is you are confident in area, If not don't do it cause you can stop your PC booting to windows if you click the wrong area in MSCONFIG screen. This would limit your task running on the CPU inturn speed up your machine keeping the NB and CPU cooler inturn the inside of your case too. Also using less power in idle mode.
Good Luck and do your updates too!
AMD A10 5800K
Biostar Hi-Fi A85S3
x2 4GB Ripjaw 1600's
OCz 240GB Vertex II SSD
X-Fi Titanium HD
AMD 7870 2GB
Acer W500 Windows8 Tablet AMD C50, 2GB, 32GB MicroSSD
AMD Phenom X2 Black Edition
Nforce 8200A AM3