we are working on the migration guide, and it will be a part of the owncloud docs
As soon as its done - we will make an announcement. For now - you can either wait or do the migration yourself.
Just execute this commands for the 9 to 10 migration:
univention-app remove owncloud82
univention-app install owncloud
I recommend waiting though.
If you do the upgrade - let me know how it went and if I could help you in any way