How do I update the sitemap in D7?
The XML Sitemap module doesn't rebuild sitemaps on every node save/load; also, it's not cached like other artifacts in Drupal. 

The module tracks XML Sitemap links and they are added/removed upon cron runs. So you'll need to run cron to rebuild your sitemap files.

You can also follow some of the steps in the Setting up your site map (7.x) documentation:


  
  Under "Inclusion" change "Excluded" to become "Included"
  To add pages linked from menus to the sitemap, visit the edit page for each menu whose items should be included (this would usually
  include the Main menu). Open the XML sitemap fieldset, and similarly
  change "Excluded" to "Included". Hit Save.
  Once that is all complete, go to Configurations --> Search and Metadata --> XML Sitemap
  Click on the Rebuild Links tab in the upper right
  Click on "Rebuild sitemap" even if the message says that you do not need to.
  Now you're taken back to the config page which shows you the link to your xmlsitemap which you can click and confirm that pages have
  been added