Yes. You'll need to 'Manage' the webinar in your channel and go to 'Edit details' in order to change the start date and/or time.
If you have enabled the email service for your channel, an automatic rescheduled notification email with be sent to those subscribers that have pre-registered to attend this webinar.
If you are not a channel owner and are speaking as a thought leader, please contact your community manager to request a date & time change for your webinar.