Sorry if this is the wrong forum, I just went to omnirom.org and there was a link to this forum.
This is a little bit weird: Omni was not preinstalled but the update(Omni) came directly from the manurfacturer (sntron.com).
In my case no recovery mode is accessible. As I've written in the 1st post, I copied the update on a sd-card and booted from it so that the updated installs automatically.
Attached is a picture of what is installed.
Thanks for any info.