George,
I have gotten the following to work at some point:
curl -s -m 5 -X PUT -H ‘Content-Type: application/json’ -d ‘{“name” : “admin”, “password” : “admin”, “newPassword” : “admin123″}’ 127.0.0.1/api/users
Where your actually doing a put on the user collection instead with the existing user “admin” and the old password “admin” and the newPassoword specified.
Let me know if that helps.
Jeff