I had the problem that I had created a lot of pages for the web-site, which was created with a sample-page as a starting point. The problem was that all the URL’s contained “sample-page”, which was undesired. It took a little while to figure out where the “sample-page” came from. I turned out to be the “slug” from the top page.
It is very easy to remove by selecting “quick edit” and setting the “slug” field to an empty sting as shown below.