Download/Upload files thru a https server

Question

I have been able to connect to a https server using

NetworkCredential nc = new NetworkCredential("user", "password");
 
WebRequest wr1 = WebRequest.Create("https://sftp.dts.ca.gov");

wr1.Credentials = nc;
 WebResponse rx = wr1.GetResponse();

however after that I am lost how do I change directories get files and send files. Any points most appreciated.