baimac

http://separatedfaithful.org/wp-content/uploads/Screen-Shot-2015-11-12-at-12.56.55-PM.png

The link above is a screen shot of my website with Chrome’s developer tools.
I’m trying to change the image size of thumbnail from 150 to 120 (or even less). From where is the 150 coming? In Atahualpa-theme settings, I have thumbnail set to 120 width and height. When I added the image to media library originally, it is about a 400px square. On the list on the list of TPG get posts, I want them to appear as 120 px (or less) but they appear as 150..
When I look at instructions for changing thumbnail dimensions
ahttps://codex.ww.wp.xz.cn/Function_Reference/set_post_thumbnail_size
it shows that I shoud edit the functions.php file. But my functions php file doesn’t look like the one in the instructions.

set_post_thumbnail_size( $bfa_ata[‘post_thumbnail_width’], $bfa_ata[‘post_thumbnail_height’], true );
else set_post_thumbnail_size( $bfa_ata[‘post_thumbnail_width’], $bfa_ata[‘post_thumbnail_height’] );
add_image_size( ‘single-post-thumbnail’, 400, 9999 ); // Permalink thumbnail size

Can you help?