Auto Generate Sitemap in wordpress

hello
I have one wordpress site. now i install google xml sitemap plugin in to my site. there was one problem in during generate sitemap for my latest post contents. and how to generate sitemap as automatic.?

1.) Use a FTP program (Filezilla) or the File Manager from CPanel and navigate to your site.

Delete these 2 files:

sitemap.xml
sitemap.xml.gz

2.) Go to your Wordpress admin section.
Under Settings got to XML-Sitemap

3.) Press the link in:
If you changed something on your server or blog, you should rebuild the sitemap manually.

And dont forget to set that file permissions.
If it set correctly, all will be done automatically. Your sitemap will be updated automatically after you update your contents