It is not necessary or recommended to delete Test Registrations in your Event before changing the Event Status to Live. When Registrations are created while the Event is in a 'Testing' Status, they are marked as 'Test' Registrations. When the Status of the Event is changed from 'Testing' to 'Live' under Plan > Event Setup > Details, all of the Test Registrations will be removed. This Test Registrations are still accessible in the Registrations to Review section at the bottom of the Event Dashboard.
** NOTE: We recommend you do not delete Test Registrations because deleted Registrations are counted against your Billable Registrations, while 'Test' Registrations are not.