There are two ways to change the column type in SQL Server:
1- Is by writing a quick code in query script.
2- Is by using the enterprise manger: SSMS (SQL Server Management Studio).
Run the following code in SQL server:
ALTER TABLE <table name> ALTER COLUMN <column name> DATA TYPE
ALTER TABLE tblExampleTable ALTER COLUMN ID INT
See Microsoft webpage for full Alter Table syntax details:
To do the changes using the second method follow these steps:
a- Open SSMS
b- Navigate to your table which you want to modify column
c- Find column and Right click the choose Modify
d- A window will open in Edit mode so that you can change the type of each column:
e- Click on Save once you are done.
Note that when you click Save, you might show the below warning message. Saving changes is not permitted:
In this case, you can change some settings to allow this save and avoid the warning. To do this simply follow these steps:
1- In SSMS, click on Tools
2- Choose Options
3- Click on the Designers section from the left side menu
4- Un-check the box for: Prevent saving changes that require table re-creation
Now try to save again and this time it will work.