The concert details you can change are after you have published your concert:
the picture
the text description
the number of available tickets
Date and Time, read more below:
If you change the concert date and time, ticket buyers can ask Be My Concert for a refund if they cannot make it for the new date and/or time.
If you're looking for how to reschedule your concert, please refer to "How do I reschedule my concert?".