What should I upgrade in order to run games like WoW at max settings?

You got great PC there. The only thing you need to upgrade is your GPU (graphic card) (maybe PSU (power supply) didn't see in your list). The best PSU Brands are Corsair, Antec and Cool Master. (don't trust low brands)

If you want to upgrade your graphic card make sure if your motherboard have an PCI-E slot. ( I presume your using integrated motherboard video card).

The best and cheap graphic card will be the GTS 250 - It will run any games in MAX (WoW will be in MAX also). I have the GTS 250 also.It requires 450 Watts PSU. But for recommended is 600Watts

http://www.newegg.com/Product/Product.aspx?Item=N8... - the GTS 250

http://www.newegg.com/Product/Product.aspx?Item=N8... - 600Watts PSU Corsair a great band.

This is the cheapest graphic card and reliable for you to play WoW and other newer games.

Hope I helped ;)

If its just WoW, than the only problem you have is your Graphic card. So what i recommend is that you upgrade to an ATI Radeon HD 5750/70 if you want to play max settings. This card costs around 110-140 dollars. The reason i say to get ATI is because it uses less power and its cheaper for quality. However if your PSU is lower than 500w you cannot use this card. (branded, if non-branded than 550w) if your PSU is 400w the best you can get is an ATI Radeon HD 5670, 5650, 5570 if you dont have money? But these will only play from high settings(first) to high-mid settings.

If your PSU is lower than that than there's no point in getting a new card.

Video card, no question. The 9300 is a low-end piece of crap.