low quality picture problem wordpress

hey there,
firstly I dont know is it right topic but I have a problem on pictures.
I added a photo to my wordpress but it’s quality has changed.
how can I solve?

Probably problem comes from add_image_size() function/

If you want to prevent WordPress from compressing files or increase how much it compresses files, you can make a change to functions.php in your Theme, or install a plugin to manage the compression level such as WP Smush.it