Need better graphics

[Volusto]

Hey i got my new computer about a week ago hoping that it would display WoW better but i haven't had an increase in Fps at all.. Any help on what i should buy to allow me to run wow on ultra?

i am running a
HP Pavilion P6000
AMD Athlon II x4 635 proccessor 2900 Mhz
Windows 7 home premium
ATI Radeon HD 4200 video card
6GB of Ram
1920 x 1080 Res