drush upwd [user] --password="newpassword"

If you happen to use drush you can use drush upwd [user] --password="[newpassword]" which (re)sets the password for the user with the specified name. (upwd is the short command version for user-password)

Example from drush: drush user-password someuser --password="correct horse battery staple" which sets the specified password for username "someuser".