Fusion 8 on Yosemite - want to extend a VM Yosemite Partition

Hello,

This video shows how to extend Partitions in OS X using Disk Utility:

17 Mac OS X Yosemite Tricks How to resize partitions with Disk Utility - YouTube

However, when I am logged in to Yosemite VM Image running in Fusion, it shows me a 42.09GByte "Macintosh HD" and 10GBytes of "Free Space" below that but the "Macintosh HD" partition cannot be modified -- cannot drag bottom right corner and the "Size" text field is greyed out.  How can this be done?

Thanks

DH