1. Set your VM OS HDD 20GB to 40GB
2. Boot your VM and use SSH login
3. Follow the command as below:
sudo su
parted
mkpart primary 20GB 40GB
print
quit
reboot
sudo su
lvm
pvcreate /dev/sda3
pvs
quit
pvscan
vgextend ubuntu1404-vg /dev/sda3
pvscan
ls /dev/ubuntu1404-vg
df -h
lvextend -L +20G /dev/ubuntu1404-vg/root
resize2fs /dev/ubuntu1404-vg/root
df -h