VBoxManage clonemedium disk inputDisk.vmdk outputDisk.vdi --format VDI
VBoxManage modifymedium disk outputDisk.vdi --resize 256000  # size in MB
fdisk /dev/sda
  d  # delete partition
  3  # delete partition 3
  n  # create new partition
  p  # primary, accept default start/end blocks
  N  # to delete signature
  w  # write changes
reboot
resize2fs /dev/sda3