I like it a lot that event cancellation is part of package, but there is a use case which should be considered.
Assume a user registers 5 people for an event. At some point the user notices that there will be only 2 persons going with him. In this case the user has no chance to change the number of people going with him. So the user has to cancel the event and start the registration again with less people.

I would like to see another button for only changing the number of people.