Thanks Asyn, I've now done that and set up a new password.
Rocksteady, I've tried again with a new password set. At 'Menu/Settings', when it asked for my password, I entered the new password but it still says it is incorrect. I was certain the previous password was correct, and when changing the password it accepted the old one as correct. Also, at 'Menu/Log in' it accepts the password. It seems the password screen at 'Settings' is not working correctly, always rejecting correct passwords. Why does it even ask me to sign in when I am already signed in?