Rename an Image in MVC Core2 Controller

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how do I rename an image in an MVC core 2 controller.

The code below is not working and nothing is done.

string savelocation = path;
            string fileExtention = System.IO.Path.GetExtension(files[0].FileName);
            //creating filename to avoid file name conflicts.
            string NewName = id.ToString();// id is actually the Primary key
            //saving file in savedImage folder.
            var savePath = savelocation + NewName + fileExtention;


            string result2 = "/uploads/" + user + "/" + Path.GetFileName(savePath);

            var stream3 = new FileStream(NewName, FileMode.Create);
            files[0].CopyTo(stream3);




            stream3.Flush();
            stream3.Dispose();

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