How to drop constraint column in sql server 2008

I am getting error to drop the default constraint column

in sql server 2008 and my Query is

Create table EmpTab
( 
EmpID int identity(1,1) primary key,
EmpName varchar(50),
EmpEmail varchar(50),
EmpContact varchar(15),
EmpHR varchar(50) Default 'HR',
EmpADD varchar(50)
)

Please tell me how to drop  EmpHR  Column

Thanks