How to Display Post Summaries on Homepage in Duster Theme

Even though I’ve made sure to check the “Show Summary” option in the Reading Settings, the Duster Theme is still displaying the entire post on the homepage.

Placing a “more” tag into the post works, but my ideal solution would automatically cut off the posts without me having to manually insert a “more” tag into each.

I’ve read here that generally, in the index.php file, one can replace
<? php the_content() ?>
with
<?php the_excerpt() ?>
but I’m not seeing this option in Duster.

Any ideas? I appreciate any help in this matter.

Thanks.