How to remove foreign key constraint in sql server?

Try following

ALTER TABLE <TABLE_NAME> DROP CONSTRAINT <FOREIGN_KEY_NAME>

Refer : http://www.w3schools.com/sql/sql_foreignkey.asp

ALTER TABLE [TableName] DROP CONSTRAINT [CONSTRAINT_NAME]

But, be careful man, once you do that, you may never get a chance back, and you should read some basic database book see why we need foreign key

Its wrong to do that in refer to referential integrity, because once its broken its not easy to turn it on again without having to go through the records and delete the ones which breaks the constraints.

Anyway the Syntax is as follows:

ALTER TABLE Tablename DROP CONSTRAINT ContName;

See MSDN:

• Delete Primary Keys
• Delete Foreign Key Relationships

To remove all the constraints from the DB:

SELECT 'ALTER TABLE ' + Table_Name  +' DROP CONSTRAINT ' + Constraint_Name
FROM Information_Schema.CONSTRAINT_TABLE_USAGE