If you have 404 page that you want to be removed from the Google Search results or you have a page that is outdated and is been crawled but now you want it to be removed, then you can do it using Webmaster Page removal tool.
Google Webmaster tool generates the list of all 404 urls that Google bot has encountered. Simply submit that link to Google removals page.
Just make sure that you provide a correct complete url for the page that has to be removed
It may take time for the requested urls to be removed, so you may see the request as pending until being processed.