string lstrFileFolder = HttpContext.Current.Server.MapPath(Com.Common.m_folderData); 
            string subFolder = System.DateTime.Today.AddDays(-1).ToString("yyMMdd");
            string newFolder = System.DateTime.Today.ToString("yyMMdd");
            string path = lstrFileFolder + subFolder;
            //判断目录是否存在，存在则改名 
            if (Directory.Exists(path))
            newFolder;
            }

System.IO.Directory.Move("源目录","新目录");  
  OR   

  项目－>引用     浏览     COM组件     Microsoft     Scripting     Runtime     ,  
          Scripting.FileSystemObject     fso=new     Scripting.FileSystemObjectClass();      
  fso.GetFolder("目录").Name="新目录名";

关于Scripting Runtime 对象的官方说明:

An Introduction to the Scripting Runtime Object Library

http://msdn.microsoft.com/en-us/library/aa155438(office.10).aspx