Changing or deleting referential integrity
You can choose any referential integrity name from the list of named referential integrity relationships in the Referential Integrity Rules dialog box to either modify or delete it.
Choose Edit to open the Edit Referential Integrity Rule dialog box with the selected referential integrity relationship filled in. You must be able to obtain exclusive access to all tables involved in the referential integrity when you modify it.
Choose Drop to delete the selected referential integrity relationship.