VM Ware partition size

I recently upgraded to a new Intel X-25 80G SSD on my 2007 MBP. While looking at what to move onto the new smaller SSD I noted that VM Ware had my virtual machine partitioned to 20 G. The settings in VM Ware however wouldn't let me shrink it to a smaller size. It said that 20 G was a minimum. I'm only actually using about 10G and would like to free up some more space on the smaller SSD. Does anyone know how I might do this if it is even possible?