Updating entities with EF (Delete, Add, Update) with one method
You shouldn't expose entities in WCF service. Every change in entity will cause WCF webservice change and incompatibility for existing consumers. I would create decicated data transfer objects for WCF webservice and use library like Automapper to handle property mapping. 

EF entities often contain various properties (example: creation date, creator info), that shouldn't be modified, but when you expose whole entities, you allow this, which in future may cause security issues.

Small example (without Automapper):

public class EventDTO 
{
    public int Id { get; set; }
    public DateTime EventDate { get; set; }
    public string Title { get; set; }
}


In webservice class:

public Event UpdateEvent(Guid sessionID, EventDTO eventDTO)
{
    using (IFSDB ifsdb = new IFSDB())
    {
        var event = ifsdb.Events.First(item =&gt; item.Id == eventDTO.Id);
        event.EventDate = eventDTO.EventDate;
        event.Title = eventDTO.Title;
        ifsdb.SaveChanges();
    }
}