How to delete unwanted block I've created a new block in my views.

Let's say the block name is 'slideshow'.

I've put the block into "Main Content" region and it's showing up.

The problem is that "Main Content" region is also displaying a list of nodes of "slideshow" with unformatted. So basically, "Main Content" region is displaying both unformatted version of "slideshow" and "slideshow"

when I inspect unformatted slideshow block, it has an id of "block-system-main".

How do I remove block-system-main ?
Are you talking about the front page or a custom view?

If you are in the front page view, you have probably set the content type for slideshow images to be promoted to front page. Disable that in

admin/structure/types


by clicking manage and in the footer untick 'promoted to front page'

and they will stop showing up unformatted.
In that case you aren't actually talking about a 'block', but the system content that is displayed in the main content block defined in the themes page.tpl.php page with

&lt;!-- Page Content --&gt;
&lt;?php print render($page['content']); ?&gt;