How to disable featured images auto crop in WordPress

If you want to show your featured images in blog in the original aspect ratio (scale images, instead of hard crop):

Edit functions.php file in theme folder by FTP (/wp-content/themes/your-theme-name/functions.php).
Search for add_image_size text in code, you will find theme images sizes code like this:
Change ALL true words to false in this part of code. This will disable crop for this images sizes in WordPress.
Save changed file on FTP (or upload it with replace if you edited local theme file).
Go to WordPress backend, Tools > Thumbnails regeneration and run process. Wait until all images will be resized.