Add disk extension to VM .vdi (VirtualBox) and resizing the root partition in Ubuntu

1. in MacOS X

cd /Applications/VirtualBox.app/Contents/Resources/VirtualBoxVM.app/Contents/MacOS/
VBoxManage modifyhd --resize 16384 "/Users/LouisBB/VirtualBox VMs/lubuntu/lubuntu.vdi"  #16384 is the new MiB size of your vdi

2. in ubuntu

sudo apt-get install gparted
sudo gparted

3. in GParted swapoff and delete swap partition, which followed to the /dev/sda1(root partition) save operation right click to root partition, move/resize resize it, and leave some spaces for your new swap partition save operation resize new swap partition save operation reboot