Change sort order of posts by categories

I have created menu items for my categories and I would like to order the results in different order than by latest posted. For instance, I have a category of "key concepts" and I would like to order the posts alphabetically. Is there somewhere I can edit the php source to do that without causing problems elsewhwere? Normally, I would edit the category.php file I assume, but this isn't part of the Clean Journal theme ... I can't see any switches in the the customization panel that would allow me to do this. Any ideas welcome! Many thanks! Jim