Refer: https://askubuntu.com/questions/703746/how-to-completely-remove-virtualbox
$ sudo apt-get remove --purge virtualbox
Run these commands to delete all virtual machines and settings and Virtual Hard Drives:
$ sudo rm ~/"VirtualBox VMs" -Rf
$ sudo rm ~/.config/VirtualBox/ -Rf
If you want to install it again. Run this command:
$ sudo apt-get install virtualbox