1) Download the latest VirtualBox software, and then install onto new server.
2) Download Oracle VM VirtualBox Extension Pack, and install it onto new server.
3) Copy all the storage files on to the same folder of the new server.
4) Copy “C:\Users\jamesh\VirtualBox VMs” folder from old server to new server.
5)Add the VM Machines to the VirtualBox on the new server.
Click Machine menu, click Add, from the Virtual Machine folder, select the .vbox file of the VM machine that you want to add (import).
6) Repeat step 5 for every virtual machine.
You can also do it by using export/import as per Oracle VirtualBox documentation. But what I have done according to the previous steps is working and fast.