This part will instruct you how to use the configuration example to resize the gadget by adding the height field (for example, height="300") to the <ModulePrefs> tag in the HelloGadget.xml file:
<ModulePrefs author="eXoPlatform"
title="Hello World"
directory_title="Hello World"
description="The simplest gadget"
height="300">
</ModulePrefs>
You can also resize a gadget through the web console as stated in Editing a gadget.