Page Update Failed; Permission Denied

Dear All,

I am trying to update my website pages, however, every time I click on update button it directs to an error pages saying the following:

PLEASE HELP, VERY MUCH APPRECIATED

THANK YOY

Warning: DOMDocument::save(/homepages/19/d492573743/htdocs/app492574229/sitemap.xml): failed to open stream: Permission denied in /homepages/19/d492573743/htdocs/app492574229/wp-content/plugins/google-sitemap-plugin/google-sitemap-plugin.php on line 84

Warning: Cannot modify header information – headers already sent by (output started at /homepages/19/d492573743/htdocs/app492574229/wp-content/plugins/google-sitemap-plugin/google-sitemap-plugin.php:84) in /homepages/19/d492573743/htdocs/app492574229/wp-admin/post.php on line 235

Warning: Cannot modify header information – headers already sent by (output started at /homepages/19/d492573743/htdocs/app492574229/wp-content/plugins/google-sitemap-plugin/google-sitemap-plugin.php:84) in /homepages/19/d492573743/htdocs/app492574229/wp-includes/pluggable.php on line 1121