If you're a BT Total Broadband customer and you want to change the password, you can go to btyahoo.com, log in there and change your password. The primary email account and the FON/OZ logins are linked. if you change your email password, your FON/OZ password will also change.
if you're an Openzone only customer, you can log into your control panel on the main page and change your password there.
All you need to do is change your primary email addresses password. H_Dawg gave ya some info there but if you can't remember your password just go to http://www.btinternet.com and before trying to sign in click on 'Forgot password' to go through and reset your password to a better one more suited to yourself. Hope this helps.