You can upgrade from Java Enterprise System (Java ES) 3, 4, or 5 to Application Server 9.1.
Upgrade to Java ES 5 Update 1.
For more details, see the Java ES 5 documentation on docs.sun.com. If you have already upgraded Message Queue to a version later than 4.1, upgrading to Java ES 5 Update 1 will cause Message Queue to be downgraded to version 4.1.
Install Sun Java System Application Server 9.1 IFR bundle.
This bundle is available with Java ES 5 Update 1 as an optional download.
If you have already installed a JDK version that is newer than 1.5.0_12, do not choose the Install Java 2 SDK (5.0) option during the Application Server 9.1 installation. Select the Reuse Existing Java 2 SDK option instead.
Use appropriate patches from SunSolve to upgrade from to Application Server 9.1.
See To Upgrade a Package-Based Installation of Application Server 9.1 for patch numbers and more details.