Increase disk size of a VirtualBox Linux guest

One possible way to increase the disk size of a VirtualBox Linux guest:

• Stop the virtual machine
• In VirtualBox menu, select File > Tools > Virtual Media Manager...
• In the Hard disks tab, Select the virtual machine hard disk. The virtual machine can be deduced from the directory path displayed when clicking on a given hard disk
• Increase the size
  
• Click on the Apply button
• Download a bootable gparted ISO image from here (for me: gparted-live-1.5.0-6-amd64.iso)
• Check the checksum
• Modify the settings of the virtual machine so that it boots on the gparted ISO image: add the image as an optical drive, check Live CD/DVD, and check that the boot order will make the machine boot on the optical drive
• Start the Virtual Machine. It starts gparted
• Using gparted, resize the relevant partition
• Quit gparted, exit
• Remove the optical drive from the virtual drive, in Settings > Storage
• Restart the virtual machine