I would switch to use SSH key pairs and forgo password authentication altogether.
It's more secure (you can disable password authentication in
sshd_config and enjoy having a drastic reduction in brute force attempts in your
auth.log) because they can create their own passphrase and if they forget that, they can just create a new key pair and simply email you their public key to append to their user's
PuttyGen is very easy to use, Mac and Linux users have
ssh-keygen built-in and is essentially two commands to generate the key and output it with
cat or whatever so that they can copy/paste (or you could wrap up in a simple bash script or Cocoa or whatever for them).
If your users have very little computer knowledge, I don't even think an FTP Server is going to fly. You should move to a Web-based file management system. Pick your scripting language/platform of choice: there are dozens of them out there. PHPfileNavigator's solid, for example.
If for some reason you're stuck with FTP, reset their password for them and send it to them out-of-band (phone call or SMS) or email if the risk/content privacy is low.