How to convert WebClient to HttpClient C# WinForms

Question

I need to convert the webclient code which is obsolte to httpclient.

using WebClient Client = new();
Client.Headers["User-Agent"] = CompanyName + "/" + ProductName;
byte[] responseBytes = Client.UploadFile("http://blahblah.com/upload.php", fileimage);
string response = Encoding.Default.GetString(responseBytes);
_ = MessageBox.Show(response, Text);

I need the exact same way to do this. I have seen other answers but none meet my needs.

Answer 1

1- read AllByte of file into upfilebytes array

2-create new HttpClient and MultipartFormDataContent

3- add byte array to content

4-upload MultipartFormDataContent content async and store response in response.

var upfilebytes = File.ReadAllBytes("fileimage");

HttpClient client = new HttpClient();
client.DefaultRequestHeaders.Add("User-Agent", CompanyName + "/" + ProductName);
MultipartFormDataContent content = new MultipartFormDataContent();
ByteArrayContent baContent = new ByteArrayContent(upfilebytes);

content.Add(baContent, "File", "filename.png");

 var response = await client.PostAsync("http://blahblah.com/upload.php", content);

 var responsestr = await response.Content.ReadAsStringAsync();

MessageBox.Show(response, responsestr);