Change the Calendar Reginal Setting Calendar Type Gour

 using (SPSite oSiteCollection = new SPSite(SPContext.Current.Web.Site.Url))

        {

            using (SPWeb oWebsiteRoot = oSiteCollection.RootWeb)

            {

                //Response.Write(oWebsiteRoot.RegionalSettings.CalendarType);

                SPRegionalSettings oRegionalSettings = oWebsiteRoot.RegionalSettings;

                oRegionalSettings.CalendarType = 6;

                oRegionalSettings.AdjustHijriDays = 2;

                DateTimeControl1.Calendar = SPCalendarType.Hijri;

                oWebsiteRoot.Update();

                Response.Write(oWebsiteRoot.RegionalSettings.CalendarType);

            }

        }