Put the following code in functions.php:

function themify_custom_excerpt_length( $length ) {
   return 50;
}
add_filter( 'excerpt_length', 'themify_custom_excerpt_length', 999 );

Use 999 as the priority to ensure that the function runs after the default WordPress filter, otherwise it would override what is set here.

To do this, put the following code in functions.php:

function custom_excerpt_more($more) {
   return '<a href="'. get_permalink($post->ID) . '">Read More</a>';
}
add_filter('excerpt_more', 'custom_excerpt_more');

The results should look like this:

In our functions.php

function new_excerpt_more( $more ) {
    return '.....';
}
add_filter('excerpt_more', 'new_excerpt_more');

We should get this: