How to Prevent Generating Image Multiple Sizes

Hi, it appears that when I add an image to Theme it is duplicating it.

When I looked on the server in the folder: (public_html > wp-content > uploads > 2016 > 02) there are tons of images there (looks like duplicates) and it appears like it is making many different sizes for each image and I didn't do that that.

This is quickly use up all of my server space. So please give me solution i have more then 100000+ images any theme is making 24 images of 1 image i don't know why.

add_image_size ( 'kt-post-thumb', 345, 244, true );
add_image_size ( 'kt-post-thumb-small', 70, 49, true );
add_image_size ( 'kt_post_blog_268x255', 268, 255, true );
add_image_size ( 'lookbook-thumb', 270, 270, true );
add_image_size ( 'lookbook-thumb-masonry', 375, 375, false );
add_image_size ( 'colection-thumb', 380, 532, true );
add_image_size ( 'colection_small_thumb', 250, 349, true );
add_image_size ( 'testimonial-thumb', 140, 140, true );

set_post_thumbnail_size( 825, 510, true );