In this blog I have described how to changed data type of existing column of table. For demonstration, I have used a table that given below.

CREATE TABLE [dbo].[EmpInfo]
(
[ID] INT IDENTITY PRIMARY KEY,
[Name] VARCHAR(50),
[Date] VARCHAR(50)
)

Syntax:

ALTER TABLE <Table Name> ALTER COLUMN <Column Name> <New Data Type> <Size Depend on Data Type>

Example:

ALTER TABLE [dbo].[EmpInfo]
ALTER COLUMN [DATE] DATETIME