Rename instance of SQL Server
Use the following to identify the name of the SQL Server
select @@servername
To change the name of the SQL Server instance:
sp_dropserver 'OldSqlName' go sp_addserver 'NewSqlName', local go
Be sure to RESTART the SQL Server service.
Easiest way is to right-click on the server in the Object Explorer in SQL Management Studio and select 'restart' from the pop-up menu.