The options for changing your site privacy are in ‘Settings’, ‘Reading’.

By default each site’s privacy is set to ‘Only registered users of this site can have access’ (please note with ClassBlogs’ the privacy is set by the tutor)

If you are considering making your site public please ensure that your site is compliant with accessibility legislation, see the accessibility page for details.  

For more details see this guide: https://docs.campuspress.com/en/articles/461-change-site-privacy