When you visit the Java download site with a 32bit web browser you will get the 32bit Java download by default. Visit the [http://java.com/en/download/manual.jsp Java download site] to download the 64bit version.
If you don't need the 32bit version of Java you should uninstall Java completly completely and install only the 64bit version. This will prevent problems where the 32bit version is automaticly selected to run Wurm.
Once you have the 64bit Java installed you can create a shortcut to start the Wurm client. Paste one of the following command lines as target for the shortcut.