Microsoft has a C# example of uploading file to FTP server in MSDN https://msdn.microsoft.com/en-us/library/ms229715(v=vs.100).aspx and Microsoft docs https://docs.microsoft.com/en-us/dotnet/framework/network-programming/how-to-upload-files-with-ftp:

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// Copy the contents of the file to the request stream.
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StreamReader sourceStream = new StreamReader("testfile.txt");
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byte[] fileContents = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd());
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sourceStream.Close();
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request.ContentLength = fileContents.Length;
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Stream requestStream = request.GetRequestStream();
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requestStream.Write(fileContents, 0, fileContents.Length);
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requestStream.Close();

It uses StreamReader to read a string from a text file, then encode the string to bytes and upload.

This document’s title has a general title “Upload Files with FTP”. However, this approach with StreamReader only works with text file. If the above code is used to upload a binary file, like a picture, the uploaded file on FTP server becomes corrupted. The general options are:

1. Call File.ReadAllBytes to read the bytes, and write to request stream:

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   byte[] fileContents = File.ReadAllBytes(filePath);
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   using (Stream requestStream = request.GetRequestStream())
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   {
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       requestStream.Write(fileContents, 0, fileContents.Length);
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   }
   

2. Use FileStream to read the file, and copy the file stream to request stream:

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   public static async Task<FtpStatusCode> FtpUploadAsync(string uri, string userName, string password, string filePath)
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   {
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       FtpWebRequest request = (FtpWebRequest)WebRequest.Create(uri);
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       request.Method = WebRequestMethods.Ftp.UploadFile;
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       request.Credentials = new NetworkCredential(userName, password);
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       // request.UsePassive is true by default.
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       using (FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
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       using (Stream requestStream = request.GetRequestStream())
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       {
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           await fileStream.CopyToAsync(requestStream);
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       }
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       using (FtpWebResponse response = (FtpWebResponse)await request.GetResponseAsync())
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       {
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           return response.StatusCode;
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       }
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   }
   

3. Use WebClient, which wraps all the above work flow:

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   public static async Task FtpUploadAsync(string uri, string userName, string password, string filePath)
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   {
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       using (WebClient webClient = new WebClient())
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       {
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           webClient.Credentials = new NetworkCredential(userName, password);
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           await webClient.UploadFileTaskAsync(uri, WebRequestMethods.Ftp.UploadFile, filePath);
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       }
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   }