Can this pci-e video card fit in my PC?

i just bought a new HP Pavilion Elite. it was $900 but came with an ati radeon HD 5450. i wanna play some games so i wanna upgrade to the 5750. on the amd site it says it requires a Pci-e 2.1 slot. how do i know if i have that? thanks|||ehm well you have to post model number and so on .... a tip btw never ever buy store assembled PCes ... much better if you do it your self and quite simpel, then you know you entire system and there isent all that plastic / metal ******* u in the *** when u open the case