This post pertains to the configuration of Weblogic Server from 32-bit mode to 64-bit mode on Solaris OS. Just in case, you have WLS 10.3.6 running in 32-bit mode and the JDK being used is installed for 64-bit mode [On Solaris OS, JDK 64-bit installation comprises of installing 32-bit JDK followed by a patch for 64-bit JDK]. 

Verification of the mode being used

One can verify the mode of Weblogic Server in the following ways

• Either check the commonEnv.sh script located at $MIDDLEWARE_HOME/wlserver_10.3/common/bin where $MIDDLEWARE_HOME refers to the install directory of Middleware. Look for the patterns - SUN_ARCH_DATA_MODEL and JAVA_USE_64BIT in the file. 
  For 32-bit mode, the parameters would appear as shown below
  SUN_ARCH_DATA_MODEL="32"
  JAVA_USE_64BIT=false
• Check the server console logs; which JDK is being used during start-up
• By checking which JDK is used by the running process of Weblogic Server

Configuration Steps

• Take a backup of the commonEnv.sh script located at $MIDDLEWARE_HOME/wlserver_10.3/common/bin where $MIDDLEWARE_HOME refers to the install directory of Middleware
• Modify the commonEnv.sh script for the following parameters: The values should be 64 and true respectively for 64-bit mode
  SUN_ARCH_DATA_MODEL="64"
  JAVA_USE_64BIT=true 
• Restart the weblogic server.

One can confirm that the JDK being used is 64-bit by looking at the Weblogic console logs during server start up or by looking at the running process.