modifying Autofocus Pro php files

Hi everyone,

The website uses the theme Autofocus Pro (child of Thematic).
I’d like the sidebar on the homepage to display only posts from 1 category.

It seems I have to change the home.php (or index.php).
However, since it’s a child theme, there is none of these files in the theme directory.

Should I simply modify the codes of the parent theme?

http://www.G10innovation.dk

Thanks