Enter either your login name or your email address and click the button. You will then shortly receive an email containing a special link. Click this link to open a page that allows you to enter a new password - on that page type in your password into both boxes and click Submit. That's it!
The link can only be used once, and expires in less than 24 hours if not used. However, you can use the procedure as many times as you like, so if you don't use the link in time just start again.