Query for altering the columns default value

I have googled a lot with no success , just need to know the query for altering the column defau开发者_如何学JAVAlt value.

1) Drop the old default value:

ALTER TABLE <TableName> DROP CONSTRAINT <DF_ContstraintName>

2) Add new default value:

ALTER TABLE <TableName> ADD CONSTRAINT
<DF_ContstraintName> DEFAULT <Value> FOR <ColumnName>