When you connect you to the web interface, it is possible to use the functionnality "Forgot password?" If you need to connect but you have forgotten your password.
The login must be a valid Email address because the system will try to send the Emaili to this address.
Click on the link "Forgot password ?"
A web page should opens asking you to enter you login and to answear to a captcha
Click on "Continue"
You will receive an Email which contain a link to reset your password :