Until now, there are still no official support to Beta2Beta upgrade.
The latest Drupal beta release is now beta 11.
For those in a wild who are running on Drupal8 beta version, here is a little instruction to help you upgrade between each beta version.
Please understand that I can't guarantee that you will be able to do this successfully or you may even lose your site! What I am telling you is something I have discovered myself, and it works for me.
Most important: Make a back up of your Drupal database and source first!