We have added .xml sitemap in September 2014. All current websites will only generate .xml sitemap files since the update. Existing sitemap.txt files will not be deleted, however they won't be updated. The .xml sitemap link reads as follows: your-domain.com/incms_files/sitemap.xml. Simply replace your-domain.com by your own domain. If the .xml sitemap file is not available yet, please login to your website, then log out again. Give it some time, the .xml sitemap file is created and updated automatically after logging out.
We have also added the "lastmod" value to the xml file. This will cause the Google crawler to visit a website much earlier if it is only rarely updated, as it will set the "lastmod" time to the time the user logs out.