How to Create/Update an EventRelation records for contacts or a Lead record

I want to create/update an EventRelation  record related to an Event record,

In salesforce I could create an Event with multiple contacts or only one Lead (limitation);

If I want to update/change WhoId Lead Contact and save I mark rows for deletion and save, and this it will not work and I get Error : EventRelation can’t be created for a Event that already has a lead
OR if I change Contacts to Lead
Error:  EventRelation of a lead can’t be created for a Event 
that has already had EventRelation of contacts or accounts, opportunities, custom objects, and other entities.

How can I handle this situation? Please help.