How to: Delete Check Constraints (Visual Database Tools)
Delete a check constraint when you want to remove the limitations on data values that are accepted in the column or columns included in the constraint expression.
To delete a check constraint
In Object Explorer, right-click the table with the check constraint, and click Design. The table opens in Table Designer.
From the Table Designer menu, click Check Constraints.
In the Check Constraints dialog box, select the constraint in the Selected Check Constraint list.
Click the Delete button.
To undo this action, close the table without saving the changes. Choosing Delete cannot be undone without losing all other changes made to the database diagram.
The constraint is deleted from the database when you save the table.