Select the "Login" button on the start page. A pop-up window for login will then appear. Click on the "forgot your password?" button, which opens a new page with an input field.
Here you can reset your password by entering the e-mail address you entered during registration in the input field and clicking on "Request password again". You will then receive an e-mail to the address you entered with a link to change your password.
With the newly set password you can now log in as usual.