How to change SQL Server Instance Name?

First collect the output of the current instance configuration. You can get the instance name stored in the SQL Server metadata.

Make sure you have backup of all the database if you are changing the production server instance name.
[sourcecode language="sql"]
sp_helpserver
select @@servername
[/sourcecode]
You can change the instance name using below query.
Default Instance
[sourcecode language="sql"]
sp_dropserver 'old_name'
go
sp_addserver 'new_name','local'
go
[/sourcecode]

Named Instance
[sourcecode language="sql"]
sp_dropserver 'Server Name\old_Instance_name'
go
sp_addserver 'ServerName\New Instance Name','local'
go
[/sourcecode]

Verify sql server instance configuration by running below queries
[sourcecode language="sql"]
sp_helpserver
select @@servername
[/sourcecode]

Restart the SQL Server Services.
[sourcecode language="sql"]
net stop MSSQLServer
net start MSSQLServer
[/sourcecode]