When you install Sun Java System Web Server 6.1 SP11 over an existing installation of Sun Java System Web Server, the installer automatically carries out the upgrade.
If you have Sun ONE Web Server 6.1 SP1 installed, point the Sun Java System Web Server 6.1 SP11 installer to the location of the 6.1 SP1 installation and then upgrade.
If you have the Sun Java Enterprise System 1 installed on your system and you want to upgrade the Sun ONE Web Server 6.1 that is part of Sun Java Enterprise System 1 to Sun Java System Web Server 6.1 SP11, refer the Sun Java Enterprise System 2004Q2 Installation Guide.