To simply remove the user account, as root use
Code:
man userdel (to see other options and usage info)
userdel -r username
I am not familiar with Bodhi, so if it uses a 'Buntu-like sudo instead of an actual root user you should probably first create a new dummy user for them to be able to login with, again as root or sudo...
Code:
[sudo] useradd -m [other options] newuser
[sudo] passwd newuser
... where other options depend on your needs, see man useradd. The -m will cause it to create the new /home/newuser directory.
The userdel command above will remove the original user's home directory and mail files, but you will have to search for other files owned by this user, if any, to delete them.
If you do not have anything really sensitive this should be sufficient. If worried about sensitive stuff on the disk then dd as recommended by others and reinstall.