Password hashing-algorythms aren't made for being reverseible. Of course you can alsways try to bruteforce them or let others do on sites like hashhunters.net. But always remember: If your passwords are crackable, you have a stupid hashing-algorythm.
What are you trying to accomplish? If it's just a lost password, you could either empty it out so only the username is required or you could simply insert a new md5 password into the db.