Change Database compatibility level

You can change the database compatibility level through Management Studio. (Go to Database Properties - Option).

Here is the script to change the database compatibility level through SQL:

ALTER DATABASE <DB_Name> SET SINGLE_USER 
GO 
EXEC sp_dbcmptlevel <DB_Name>, 100; 
GO 
ALTER DATABASE <DB_Name> SET MULTI_USER 
GO

In above script change <DB_Name> with Database Name (you want to change the compatibility level).

Compatibility Level :

SQL Server 2008 : 100
SQL Server 2005 : 90
SQL Server 2000 : 80
SQL Server 7.0 : 70