To change your password, first go to your profile and press "Edit profile". From here you can go to "Password" and enter your current password. Then you can enter your new password, press "Change" and your password will be updated.
To reset your password, first press "Forgot password" in the login area. Then enter your e-mail address and request a link. Once you receive the email, the link will be valid for one hour. Now press "Reset password". You will then be taken back to the app where you can enter your new password.