How to access ubuntu wubi installation

I installed ubuntu/wubi nearly a year ago on my windows 8 pc. It has been sitting on a separate partition untouched since then. I am trying to access it again as I'd like to use Ubuntu now. I cannot figure out how to boot to Ubuntu. When I go to "msconfig" -> "boot". I only see an option for Windows. The Ubuntu file hierarchy looks like this: D:\ -> ubuntu -> disks, install, winboot The disk file root.disk is about 18gb. Any help is greatly appreciated.