Just an FYI, Catalina.bat is not utilized when running tomcat as a service. here is the method to change the JAVA_OPTS for tomcat running as a windows service.

Open Services and click on the Tomcat service. Make a note of the service name (most likely Tomcat6).
cd to the Tomcat bin directory
Run the command

tomcat6w //ES//Tomcat6 (substitute your service name if different)

Click on the Java tab

Add the options (each on a new line) to the Java Options box and set the initial and max memory to 1536 and 2048

-XX:MaxPermSize=256m -Djava.awt.headless=true -Djava.net.preferIPv4Stack=true

Click apply

Click on the general tab and restart the service