Shower/tub diverter

I have a three handle tub/shower that is running at the same time. I took the handle and metal cover off. When i ran the water, i could also see water spewing behind the plastic valve. I need help because i dont know how to remove this plastic valve. Any help or info will be greatly appreciated. Here is a pic of the valve.

Picture's too small and a picture of the handles and "metal cover" might help, because we don't know what you mean by "i could also see water spewing behind the plastic valve".

Need better photos. "Spewing" is never a good thing when we are looking a pic inside the wall!

Ok, I will get more pics.