Hello kyo, I’d recommend that you watch the YouTube videos that Unreal has posted: http://www.youtube.com/playlist?list=PLZlv_N0_O1gaCL2XjKluO7N2Pmmw9pvhE They’re very user friendly, and will help you grasp the concepts within the engine in a much shorter timeframe.
I cannot say anything regarding the speed at which it runs on your computer, however bosung90’s answer may help, and as Baesky has said, you cannot get a refund.