How do i change my windows XP back to a vista?

My computer (compaq Presario c700) used to be a Vista computer. But I decided to change it to windows XP home edition 2002, because I thought it had more stuff to offer. But know i want to go back to Vista and I have no clue how to go about doing it. Also i tried looking for a vista installation disk that I thought would come with the computer and all that came with it was a picture of a disk saying that I should back up my files encase this happened...