You can also modify the settings for the network. But that's where I'm confused; you say you want to change userid and password? Are you logging in through a password-protected gateway hotspot (the kind that asks for ID and password through a webpage)? If so, forgetting the network won't forget your login credentials. You'd have to clear them either on your browser or contact the networks admin to delete your info from their system if it's automatically matching your MAC address to your 'old' user ID.