You can change or remove column defaults using the same form of the ALTER TABLE statement you used to create the defaults.

The following statement changes the default value of a column named OrderDate from its current setting to CURRENT DATE:

ALTER TABLE SalesOrders
ALTER OrderDate DEFAULT CURRENT DATE;

You can remove column defaults by modifying them to be NULL. The following statement removes the default from the OrderDate column:

ALTER TABLE SalesOrders
ALTER OrderDate DEFAULT NULL;