using CMS.SiteProvider;

using CMS.CMSHelper;

using CMS.WorkflowEngine;

...

        // Code name of the site

        string siteName = "mysitecodename";

        // Delete records in CMS_Tree and CMS_Document

        DocumentHelper.DeleteSiteTree(siteName, null);

        // Delete other dependencies and the site

        SiteInfoProvider.DeleteSite(siteName);

        lblInfo.Text = string.Format("Site '{0}' has been deleted.", siteName);