How do I Edit the symbol on one of the default topics?

Changing the image on a topic button on the main page: 
Because the modify button allows you to show and hide topics on the main page it does not function for editing.  You must first go to the topic page and then use edit to make changes to the image in the Thumbnail at the bottom of the topic page.  The thumbnail on the Main Page does not update until you close and reopen the topic after making the change