1. if you are using Youzer you can find it on the path below :
Wordpress Dashboard > Youzer > Extensions Settings.
2. If you are using only Buddypress you can find the settings page on the path :
Wordpress Dashboard > Settings > Buddypress Extensions.
3. From the 'Membership Restrictions' tab, choose the 'Restrictions Type' from the drop down then select the user role and click the 'Show Settings' button to see all options available.