How to change CentOS password

First, you need to log in SSH or Putty to your server

then use command passwd to change the password. below example is changed the root password for a Centos:
[root @ VM ~]# passwd   (Changing password for user root.)
New password:    (You should type your new password here)
Retype new password:    (You should retype your new password again)
[root @ VM ~]# all authentication tokens updated successfully.  (Your password change successfully)