Delete first picture in the Post if taken as Thumbnail | CyberSEO Pro | Support Forum

Most of modern themes have such an option, so they allow you to enable or disable featured images in posts. E.g. they (the featured images) can be shown as thumbnails at your index page, but be hidden in single posts. Take a look at Login to see this link theme.

Unfortunately some theme developers don't care about users like you (and me too) who don't want to see any featured images in single posts. In this case you just have to take the theme source and fix the single post template manually. There is no other way to do it because your theme is the only part of your website which decides what, where and how must be displayed.

P.S. I do custom coding and I can modify your theme. I do it for a very affordable price, so please contact me if you are interested.