Log into your google account on your browser, then hover your mouse over the lower right corner of the page you want to edit, and click the pencil link that appears. Once you click this link, you will enter editing mode. You can make any edits you need then press Publish on the top right to save your changes. Details on how to do specific things on the site are available in the google documentation below. If you have any problems, contact Paul Stechschulte <paul.stechschulte@mchs.com> . Your google account has to be set as an editor before you are able to edit the site.
Google Documentation: How to edit Google Sites