How to change thumbnail images in Wordpress?

Question

Images

I want to create an image gallery on a dynamic Wordpress page, but the images are always cropped to 150x150 px, but I need at least 300x300 .
tried: in settings - media files - thumbnail resizing doesn't work.
+ there is code in functions.php

if ( function_exists( 'add_theme_support' ) ) {
  add_theme_support( 'post-thumbnails' );
    set_post_thumbnail_size( 500, 500 );
}

it is needed to display images of certain sizes on the blog page.
In general, I don’t know what to do already, tell me please how to be

Answer 1

thumbnail resize not working

After changing the parameters, you need to regenerate the thumbnails, for example, using the Regenerate Thumbnails plugin .