Make front page shows only summary of posts(7 posts)

Hi there,

I wanna make my front page shows only summary of posts. The template is Twenty-twelve. It shows the full post now. I have replaced
<?php the_content(); ?>
with
<?php the_excerpt(); ?> in content.php. But the result was not good. Don’t know how to do with it now.

Can anyone help me on this?

Many thanks.