Users Password Change

Is it possible for a user to login in with the SFTP client and change their password?

How do you do this?

What I'm trying to set up is a guest user account ... the administrator of that guest user account wants to change the password and give it out adhoc, then when finished change it to something else again... I don't want to give him access to the server or let him have SSH ability ... he's not technical... so if he could change it at the SFTP client level, he could login as that guest user and change the password

Thanks

I have added an answer to documentation. Let me know if you find it useful (I fear that you would not :-))