Cannot upgrade

Hi, I bought FCPX last year and my iMac has ATI Radeon HD 2600 Pro 256 MB. I love this app and been using it for video editing just fine till today when I try to update it, it show " We could not complete your update, Your video card does not meet the minimum requirements! What? Why now, is this mean I have to upgrade my video card or buy new Imac? If Yes how much will cost me and what kind of video card does FCPX requirement? Kindly help please.