Why do you need that?
No, Disk Utility can't help with VM disk space assignments.
Disk Utility is for the disks you use, HDDs, SSDs, USB flash memory thumb drives and ODs.
As Windows is installed via VM, it gets a certain amount of disk space assigned from Parallels Desktop (or the amount you chose), and it can't be the entire capacity your SSD has, as VMs are stored in a file or several files (accumulating to 64GB in your case), thus having a Windows VM with 256GB would mean, the file(s) could be 256GB in size.
Again, why do you need the VM to have 256GB of disk space capacity?