Try to find the file's location with
Maybe as root,
sudo locate VBox.sh
I apologise, the file you need to find is the .run package (auto execute) shell file.
then tack the uninstall command at the end.
sudo sh VirtualBox (press tab for bash-autocomplete)
(on my system)
sudo sh VirtualBox-3.0.2-49928-Linux_amd64.run uninstall
This part may be different for your version...
substitute 3.0.4 and hit tab for autocomplete...
I hope this helps you, btw,
Why do you want to uninstall vbox?