Change instance name of SQL Server

It turns out that after you've changed the Windows Server's name, the underlying SQL Server's instance name is not changed accordingly, although you can see an instance name same with the Windows Server's is displayed in the SSMS.

Everything else might work fine until you want to set up replication/distribution on this server. An error message like "SQL Server replication requires the actual server name to make a connection to the server. Connections through a server alias, IP address, or any other alternate name are not supported. Specify the actual server name, ‘old_name’. (Replication.Utilities)" is popped right into your eyes.

To see the old instance name, you can use "sp_helpserver" or "select @@servername" and to change the instance name once and for all, the following script has to be executed:

sp_dropserver 'old_name'
go
sp_addserver 'new_name','local'
go

A detailed and better formatted how-to article can be retrieved from here.