BuddyPress.org

First, please read this entire thread (all the posts) at least two times through before starting: https://buddypress.org/forums/topic.php?id=1994

Then read through these links:

https://codex.wordpress.org/Upgrading_WPMU

https://buddypress.org/forums/topic.php?id=1285#post-9999

http://subversion.tigris.org/faq.html

https://codex.buddypress.org/developer-docs/installing-through-svn/

Once you’ve done that, have a SVN client installed, and feel confident, go back to the first link in this post and follow the instructions.

From where do I get the most recent versions?

Those links are provided in the detailed instructions contained in the first link above.