Rename the physical server by going to the "Identification" tab of the "Network" properties window (available from Control Panel) if you are running Windows NT 4.0. If you are running Windows 2000, go to the "Network Identification" tab of the "Computer" Properties windows (available from Control Panel).

Reboot the server.

Run the SQL Server setup program. At some point early in the installation you will be prompted to "Upgrade" SQL Server. Answer "yes" to this question. After a very short period of time, you will be prompted that the installation is complete.

Reboot the server.

Run this stored procedure
sp_dropserver <old server name>

Run this stored procedure:
sp_addserver <new server name>, local

Once you have completed all these steps, SQL Server will now recognize its new name. But keep in mind that this procedure is only for SQL Server. It will not affect how other software running on the server will be affected by the name change. If you have clients who are pointing to your server (including DSNs), they will also have to be changed to point to the new SQL Server name.