To change someone else' password, use:
To change another user's password in the same domain
To change another user's password in a different domain
passwd -D domainname username
When using the passwd command in an NIS+ environment (see "The passwd Command and "NIS+ Environment"") to change someone else's password you must have modify rights to that user's entry in the passwd table (this usually means that you are a member of the group for the passwd table and the group has modify rights). You do not have to enter either the user's old password or your password. You will be prompted to enter the new password twice to make sure that they match. If they do not match, you will be prompted to enter them again.