change constraint

Hi all, 

how do I change constraint? 

current: 

 CREATE TABLE [dbo].[table1](
 [column1] [nvarchar](50) NOT NULL,
 [column2] [nvarchar](200) NULL,
 [column3] [ntext] NULL,
 CONSTRAINT [PK_GPB_RULE_INFORMATION] PRIMARY KEY ( [column1])
);

should be: 

 CREATE TABLE [dbo].[table1](
 [column1] [nvarchar](50) NOT NULL,
 [column2] [nvarchar](200) NULL,
 [column3] [ntext] NULL,
 CONSTRAINT [PK_GPB_RULE_INFORMATION] PRIMARY KEY ( [column1, column2])
);

How do I perform this change without deleting table?