If you forgot your password, you press the according link on the homepage. After you put in your mail or user name you'll receive a one-time login to your profile page.

In formular to change your password your user name and e-mail address is already filled in, but when you change your password you'll receive the folling error messages:
"Your username already exists"
"Your e-mail address already exists"

Thoes messages makes it impossible to change your password.