BuddyPress.org

First, always read the readme.txt files that come with WPMU and BuddyPress.

Second, see these links:

https://codex.buddypress.org/getting-started/upgrading-from-10x/

https://codex.buddypress.org/how-to-guides/upgrading-a-buddypress-1-0-theme-for-buddypress-1-1/

https://buddypress.org/blog/news/the-new-buddypress-theme-architecture/