1. Install a virtual helper instance from a template.
2. Shut down the server which systemdisk should be extended.
3. Grow the VM disk via vmkfstools.

3.1 Commit or remove all snapshots.
3.2 Connect to the VMHost via putty.
3.3 Go the the directory where the VM file is placed ( /vmfs/volumes/vm_name/vm_name )
3.4 /usr/sbin/vmkfstools -X new_sizeG vm_name.vmdk

4. Add this disk to the helper instance.
5. Use diskpart to extend the partition of this disk.

5.1 diskpart <ENTER>
5.2 list volume <ENTER>
5.3 select volume “ID of volume” <ENTER>
5.4 extend <ENTER>

6. Shutdown the virtual helper instance.
( Because disks can’t be removed from running virtual machines )
7. Start the instance that systemdisk has been extended.
8. Destroy the virtual helper instance.