upgrade VirtualBox

VirtualBox Linux policy

Oroacle does not support the Ubuntu fork of VirtualBox.
install the official version from virtualbox.org along with the matching extension pack from virtualbox.org
add your user name to the vboxusers group on the host and reboot.

update VirtualBox

with the update manager
or
in the case you have update problems with Virtualbox, you want a more recent VBX version then the one approved or want to downgrade :
download the wanted version (will be .deb) from https://www.virtualbox.org/wiki/Linux_Downloads
Then sudo apt-get update && sudo apt-get upgrade
+ install the dep package

check versions

VirtualBox : main app > help > about
Virtualbox Extension Pack main app > File > preferences >

Virtualbox Extension Pack

The extension pack is needed for sharing between host and guest, 3D support, extended USB support and more.
see Virtualbox Extension Pack

VBoxGuestAdditions

a new vbx update also does not update the vbx guest additions
you have to download the corresponding iso file , and re-install in all machines (yep)
see Virtualbox Guest additions