We developed a website with basic URL structure with less content, title and meta description. The URL what very basic and was SEO Optimized. Google indexed our website and all pages in search results. Now after making some research on content, keywords and description. We changes the full content of our website with new title, Keywords and URLs. We even deleted old sitemap and generated new one and submitted in GWT. But Google is still crawling old URLs and showing 404 error in webmaster tools. We then tried to remove those URLs in Google webmaster tool and But still the old urls are not removed from Google index. Can anyone help you fix this ASAP. 
Permanently remove URL of a website which no longer exist in website
seo;google search console;url rewriting;google index;crawl errors