paras-d@Paras:~$ sudo dpkg --purge --force-remove-reinstreq virtualbox virtualbox-qt virtualbox-5.1
(Reading database ... 212433 files and directories currently installed.)
Removing virtualbox (5.0.24-dfsg-0ubuntu1.16.04.1) ...
Purging configuration files for virtualbox (5.0.24-dfsg-0ubuntu1.16.04.1) ...
Removing virtualbox-qt (5.0.24-dfsg-0ubuntu1.16.04.1) ...
Purging configuration files for virtualbox-qt (5.0.24-dfsg-0ubuntu1.16.04.1) ...
dpkg: warning: ignoring request to remove virtualbox-5.1 which isn't installed