Wordpress图库以全尺寸而不是缩略图显示图库中的所有图像

Right now my page load file size is 350mb... for a website...

The reason is that the gallery is loading in the full size 4000px+ images when they are actually a mere 250px in the page:

Is it possible to display the smallest thumbnail, or even the large image until the user clicks on the image.

I know PHP but I don't know Wordpress, so I would be happy to write this myself if I could understand where to make these changes.

So I would like to change the galleries code to only display thumbnails in this preview view as seen in the photo.

Please see the documentation for https://codex.wordpress.org/Post_Thumbnails. When you're outputting an image, you can set the desired size on several presets.

Relevant code from the documentation below.

// without parameter -> Post Thumbnail (as set by theme using set_post_thumbnail_size())
the_post_thumbnail();

the_post_thumbnail('thumbnail');       // Thumbnail (default 150px x 150px max)
the_post_thumbnail('medium');          // Medium resolution (default 300px x 300px    max)
the_post_thumbnail('medium_large');    // Medium Large resolution (default 768px x 0px max)
the_post_thumbnail('large');           // Large resolution (default 1024px x 1024px max)
the_post_thumbnail('full');            // Original image resolution (unmodified)

the_post_thumbnail( array(100,100) );  // Other resolutions