Few parts to this..
1) Firstly to get above 2TB you need to use the command line rather than GUI as it limits you to 2TB.
(e.g. resize to a 3TB drive image)
VBoxManage modifyhd '\path\VM.vdi' --resize 3000000
2) Use gparted to create partition or expand a partition
3) Use the following for getting disk details for a logical volume
sudo lvdisplay
From the uotput you can get the device LV Path
e.g. /dev/ubuntu-vg/root
then to extend to a given amount (e.g. 700GB)
sudo lvextend -L 700G /dev/ubuntu-vg/root
then expand the file system
sudo resize2fs /dev/ubuntu-vg/root
Note:
Substitute dev as appropriate
