Call server side method using javascript

Call server side method using javascript ServerSide Method:- 

System.Web.Services.WebMethod] public static string SetDownloadPath(string ID) {   
                     HttpContext.Current.Session["logo"] = ID; return ID; 
} 

Javascript To Call:- 
PageMethods.SetDownloadPath(id);

 Need To change in Following:- 

EnablePageMethods="true"