If need to reset the server level collation without reinstalling the server, the following is a way.
1. Stop SQL Server services from services
2. Run the following command from the installation folder: C:\Program Files\Microsoft SQL Server\MSSQL12.MSSQLSERVER\MSSQL\Binn
sqlservr -m -T4022 -T3659 -s"MSSQLSERVER" -q"Latin1_General_CS_AS"
[-m] single user admin mode
[-T] trace flag turned on at startup
[-s] sql server instance name
[-q] new collation to be applied
3. At the end of the sequence you should receive the messages: “The default collation was successfully changed and Recovery is complete” and “This is an informational message only. No user action is required”.
4. At the command prompt type Ctrl + C to shutdown SQL Server and then type Y to confirm you want to shutdown SQL Server
5. Now restart the SQL Server and SQL Server Agent Services