The file sitemap.index.xml can not be overwritten

[Hanhan1989]

The file sitemap.index.xml can not be overwritten. It shows me the following message Cannot create sitemap. File '/var/www/html/sitemap.index.xml' already exists.

I have to put this code before new Sitemap( )...

   if(file_exists('sitemap.index.xml')){
        unlink('sitemap.index.xml');
    }