Its important that you appreciate the difference between encryption and hashing.
Encryption uses keys to encode and decode data. Given a key it should be possible to unencrypt the data
Hashing is a one-way function where it should be impossible to obtain the original value of the data. Hashed data is used by hashing plain text and seeing if the result is the same as the stored value
Passwords are hashed. They should not be encrypted.
So, to answer your question, you cannot decrypt passwords
http://www.securityinnovationeurope.com/blog/whats-the-difference-between-hashing-and-encrypting