A couple of ways
The best thing to do is just add yourself as a member of the group, this will allow to see all your Virtual machines and use USB as well
sudo adduser ´whoami´ vboxusers
Reboot the machine or the services.
Press ALT + F2 then type gksu VirtualBox (case sensitive)
Other way is to create a launcher:
Command: gksu VirtualBox
Tags: VirtualBox ubuntu