I know the answer. I worked on it without any documentation.
In the case of edit current and following -
- you should create new Event
- re-assign (re-relate) all previous child events to the new since new date.
- Change End date of old event-series to the current new date of new-event-series. In this case old series ended for example at today 12PM, new series starts at today 12PM, for example. User will not known about internal changing of relations or changing something else