The best and safest way is to reinstalling the SQL Server with required collation.

other step:( FROM MSDN)

Make sure you have all the information or scripts needed to re-create your user databases and all the objects in them.

>>Export all your data using a tool such as bulk copy.

>>Drop all the user databases.

>>Rebuild the master database specifying the new collation in the SQLCOLLATION property of the setup command. For example:

start /wait setup.exe /qb INSTANCENAME=MSSQLSERVER REINSTALL=SQL_Engine REBUILDDATABASE=1 SAPWD=test SQLCOLLATION=SQL_Latin1_General_CP1_CI_AI

>>Create all the databases and all the objects in them.

>>Import all your data.