ADMIN: System → Configuration → Google Sitemap Tab
Before you configure this function, you may want to read more about creating Google Sitemaps for Magento sites.
The Frequency settings provide general information to search engines on how often web pages are updated and thus need to be reindexed. The Prioríty settings lets the search engines know what kind of pages you deem most important for the crawlers to index. For more details on these settings, visit http://www.sitemaps.org/.
These settings control how often Magento automatically regenerates its Google Sitemaps to ensure that they are current.
Set the Enabled setting to Yes to activate automatic regeneration of sitemaps. Use the Start Time and Frequency to specify how often you want the sitemaps to be regenerated.
Use the Error Email settings to define an e-mail recipient for error messages from the automatic sitemap regeneration process.
Note: To use Magento’s automatic generation of Google Sitemaps, you must activate the Magento Cron service.