only showing digest in index page

Now when I access my website i can see the full page of every artical. is there a way that i can just see the digest of every article from the index page of zbench theme. thanks.

PS, i know we can add “more” in every article, however i want to change all articles one time.

PS2, I read somewhere that we can use command below to replace <?php the_content(); ?> in the index page, but seems i cannot find <?php the_content(); ?> from any page of zbench themes.

<?php if(is_category() || is_archive() || is_home() ) {
the_excerpt();
} else {
the_content(‘Read the rest of this entry »’);
} ?>