If you'd like to select a new password (or you've just forgotten you're old password) you can request a password reset email from the login screen of the app. There will be a "forgot password" option below where your login credentials are requested. This will take you to a webpage where you can type in the email address associated with your profile and an email with next steps on resetting your password will be sent to your inbox.
If you'd like to select a new login PIN you can do so on the "Security" settings of your app. First toggle the function off, then toggle on again. You'll be automatically prompted to select a new PIN!