If you want to change default collation of Sql Server :
1-Make sure you have all the information or scripts needed to re-create your user databases and all the objects in them.
2-Eport all your data using a tool such as bulk copy.
3-Drop all the user databases.
4-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=<SA Password> SQLCOLLATION=SQL_Latin1_General_CP1_CI_AI