1. Power off the virtual machine.
2. Right-click the virtual machine, and click Migrate.
3. Click Change datastore.
4. Click Next, and select a datastore that is not the same as the current datastore.
5. From the dropdown, select the Thin Provision virtual disk format.
6. Click Next, then Finish. You can monitor the progress of the conversion in the Tasks and Events view in vCenter Server.