// tree provider

CMS.TreeEngine.TreeProvider provider = new CMS.TreeEngine.TreeProvider(CMS.CMSHelper.CMSContext.CurrentUser);

// get document with specified site, alias path and culture

TreeNode node = provider.SelectSingleNode(CMS.CMSHelper.CMSContext.CurrentSiteName, "/News/MyFirstNews", "en-us");

if (node != null)

{

  // change some values

  node.SetValue("NewsSummary", "Some changed summary.");

  node.SetValue("NewsText", "Some changed text.");

  // Update the document

  node.Update();

}