I did what is written in the Windows installation link to update to the current 2.0 Release and I failed. System was not running at all and stopped with an error. triede several times. Then I resored the backup.
What worked is to delete only the userdata/tmp and /cache, I left alone the other files.
Then overwrite the runtime folder with the new runtime.
This works fine. On the first start it seems not to load the sitemap, one restart and everything is fine.