Delete a
To delete a check constraint
-or-
Open the Table Designer for the table containing the constraint, right-click in the Table Designer, and choose Properties from the shortcut menu.
Caution Choosing Delete will result in an action that cannot be undone without losing all other changes made to the database diagram. To undo this action, close this database diagram and all other open database diagrams without saving the changes.
The constraint is deleted from the database when you save the table or diagram.
Attaching a New Check Constraint to a Table or Column | Check Constraints | Constraints