I installed Windows 10 on VMWare and I set its capacity as 60 gigabytes. Now I only want it to have 30 gigabytes and reclaim those 30 gigabytes for my mac. How do I change that?
You can use the C:\Program Files\VMware\VMware Workstation\vmware-vdiskmanager.exe command line utility to create a new VMDK file with the lower capaacity.
Assuming that the utility is in your path and you are in the directory with the VMDK, make sure that the virtual machine is powered off and then issue a command like this:
vmware-vdiskmanager.exe -r sourceDisk.vmdk -s 30GB -t 0 destinationDisk.vmdk
sourceDisk.vmd and confirm that everything works. (If it doesn't, you can simply restore the original VMDK file.)
Note that this does not touch the original VMDK file, it's only a VMDK copy that's created.
Also, this is not a sector-by-sector copy. All data is copied from the original, regardless of its location. Therefore, no data will be lost so long as the destination disk size is large enough to accommodate all of it.
In effect, copying the VMDK file to one that's smaller with this tool automatically performs a partition resize and a Compact during the process. This is safe because VMware is aware of its own virtual disk structure. It's the same underlying technology used by VMware Converter when it creates a cloned virtual machine with a differently sized disk.