Deleting a Blog
As a Blog contains Blog Posts, a Blog can only be deleted when it has no posts left.
To delete an entire Blog, visit Content > Blogs > Blog Posts and select all posts from the Blog you wish to delete (to do that quickly, you can use the Filter option to view only the posts of a given Blog). After selecting them, go to Edit Selected Blog Posts > Delete Selected Blog Posts.
When there are no posts left, you may then go to Content > Blogs > Blogs to delete the Blog record itself, which will remove the Blog URL from the website.