[Hugo Ashmore]

I should have been more literal .

In WP set up to run as Multi Site you have a Super Admin set of links one of which is ‘Options’ if running as single WP then that isn’t available and you need to use the Settings > General link as Paul described.

Worth bearing in mind BP is a registration/member led application it is nothing without ability for members to sign up but traditionally WP was a single bloggers tool and probably most never allowed or wanted people to sign up to the blog but simply place comments to posts so default state is registration disabled.