How to unistall and delete Ubuntu installed using Wubi

I was told a while back to get a Linux based OS and I just got around to it. Ubuntu, for the 15 minutes that it functioned, was great! Then I got a message about a crash, though before I could read it the OS, well, crashed. Now I can't use my Ubuntu OS to any extent. Everytime I use it it freezes after I enter my name and password. If I don't enter them and select "options' in the lower left hand corner, it says that the "greeter" is not working, and goes into an endless loop of check it and telling me this. WHen I installed Ubuntu I wasn't sure what I was doing, and selected demo and full installation, and it did the aouto partitioning of my hard drive. Now I can't find Ubuntu anywhere in my computer exept on the screen that allows me to choose one of five things (abriviated for ease of my typing) "Ubuntu", "Ubuntu Recovery", "Ubuntu Test", "Vista Loader", or "Vista Loader". The Vista operations still work fine, but I would very much like to delete the malfuntioning Ubuntu OS, so that I can at lease regain that memory space to use in a proper installation of either Ubuntu or another Linux OS. Any suggestions oon how to do this?