On my VirtualBox I cannot resize my macOS Sierra 10.12 partition. When I laucnhed DIsk Utility there was text at the bottom: "...This volume has 23.24 GB used space. You can not remove the first volume on the disk. This volume can not be resized." Also "Size:" box contains value 31.4 (GB) that I cannot change. Although I have free space also 31.4 GB.
How to increase this partition? Thanks in advance.