If you go into your themes folder, i.e. blog/wp-content-/themes/default and then open up your index.php file, you will see (approx line 40) the following code or similar
<? php the_excerpt(); ?>
change this to something like
<?php the_excerpt_rereloaded('80','More','all','plain','no'); ?>
And that should do it, save it and upload it to your website.
I have a similar thing running on https://www.apograph.com/blog
