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