Hey ,
So I do not know if this is an problem for me or I do not know the settings correctly . So when I open the VM (Oracle VB ) and when I try to expand the window , the exterior frame expands but the actual screen size remains the same as shown
Hi 
not sure how it works on virtualbox, on vmware we have vmware-tools and on kvm we have qemu-guest-agent. Probably VirtualBox Guest Addons can help with that.
I hope someone that do have experience with VirtualBox to respond to this post for completion
If you haven't tried this already, you may also need to change the Display resolution in Control Center > Displays in UM.
Virtualbox guest additions should fix this, while your machine is running, in virtualbox menu click devices -> insert guest additions cd image, it should download .iso, then open autorun in your vm. And you probably will need to install some packages in your vm as well - #apt install gcc make perl IIRC.