If you use VMware converter you can safely shrink the disk.
So do I Export back to the same vCenter > resize the disk and give it a different name in vCenter > then delete the original?
That would work
Is there a way to do it without creating a whole new virtual machine?
shrinking a disk is best done using converter as stated. Any other method, to me, just would not be safe.
Assuming you mean to conver the disk to Thin as in thin provisioning, rather than actually change the size under Edit settings for the VM, you can do this with svMotion.
If you actually want to shrink the disk, so the guest sees a smaller disk... Not sure.
If you are in Windows, I believe you can defrag (probably need a 3rd-party tool to move everything to the front of the partition), then use diskpart (or Disk Mgmt if you're on 2008) to shrink the partition. Then, you might be able to use VMware tools to shrink the VMDK file.
Of course, I haven't tried it myself yet. It's a fairly common technique, though most often applied when the OS is offline by using a LiveCD or mounting the HDD/VMDK to another system/VM.
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Sounds good. I used converter and it worked. Thanks.