how to decode wordpress password hash?!

how can we decode this?

Short answer… you can’t. It is deliberately one-way encrypted.

You can reset the password using MD-5 directly in the database. When you next login, WP will re-encrypt it using its own password encryption class.
http://codex.wordpress.org/Resetting_Your_Password
Video: http://www.francescolanza.com/2007/10/24/password-admin-reset/

in the table of admin (wp_users) in your database add a new key of verefication (user_activation_key) example of key “abcdefgh”
then in your url try this domaine.com/wp-login.php?action=rp&key=abcdefgh&login=admin
the login=admin i mean your login if you use admin if your admin is user123 the url will be like this domaine.com/wp-login.php?action=rp&key=abcdefgh&login=user123 then you can change your password
thxs!