Showing Excerpt in Index Page

use this https://www.ads-software.com/extend/plugins/advanced-excerpt/
Don’t forget to use single page for the blog

I already use advanced excerpt, and it works fine for themes which use excerpt for the main page blog view. Some themes have an option to switch from full post to excerpt view; but some do not have. I want to know where in the theme code defines this.

I got the solution. the_content() in the Main Index Template (index.php) should be changed to the_excerpt(). ??