There are several ways to delete Instant Database records.
1.The easiest way is from the IDB screen. Display the record. Once displayed the Delete button will appear to the right of the Existing Records list (upper right corner). Just click it.
2.You can open the folder in which your IDB records are saved and manually delete any records you wish.
The display of Existing Records is always 'dynamic'. Any records not present when Pathagoras next reads for the files won't appear in the list. (Exception: if the record was one of your last 9 used, the name of the record will still appear 'above the line' until you either clear that list or the record works its way down and eventually off the list.)