Edit Sidebar Template

I just downloaded Event Calendar/Scheduler plugin for the latest version of Atahualpa. In order for the calendar to work in the sidebar, it's telling me to do the following:

SideBar installation

To have the list of oncoming events on the sidebar, you can add the next line into sidebar's template

<?php if (function_exists('scheduler_sidebar')) echo scheduler_sidebar(); ?>

Where exactly do I go to do this? I've tried going to the theme editor, but wasn't sure exactly what to look for. Any help on this item would be appreciated.

Thanks!