How to change Java version used by TOMCAT?

When you open catalina.sh / catalina.bat, you can see :

Environment Variable Prequisites

JAVA_HOME Must point at your Java Development Kit installation.

So, set your environment variable JAVA_HOME to point to Java 6. Also make sure JRE_HOME is pointing to the same target, if it is set.

Update: since you are on Windows, see here for how to manage your environment variables

You can change the JDK or JRE location using the following steps:

1. open the terminal or cmd.
   
2. go to the [tomcat-home]\bin directory.
   ex: c:\tomcat8\bin
3. write the following command: Tomcat8W //ES//Tomcat8
4. will open dialog, select the java tab(top pane).
5. change the Java virtual Machine value.
6. click OK.

note: in Apache TomEE same steps, but step (3) the command must be: TomEE //ES