Before we start to submit the sitemap to google using webmaster tools, please make sure that you already installed the Google XML Sitemaps plugin in your wordpress blog and already been registered to Google webmaster tools account. Please refer to below pictures and steps:
1. Please make sure that your wordpress blog sitemaps has been generate automatically by Google XML Sitemaps generator.
2. Please log in to Google Webmaster tools account and go to dashboard.
3. Click Submit a Sitemap.
4. Enter sitemap.xml at the provided form then click Submit Sitemap.
5. The message sitemap.xml has been added as a Sitemap will appear at the top of the dashboard and please make sure that the status column is success.