The auto update didn't work for me either. After more then a year it never auto updated it for me. So I'm glad I found this topic and now know how to do it (manually). I assumed I had to remove my micro SD card and put it my PC and use the software to 'update' it. This is such a convenience that you can do it from the OS itself.
I seem to remember that with OpenELEC you had to do it the way I just described, so even because the auto update doesn't work (for me) this is a huge step up for me. Thanks LibreELEC team!