ASP.net HTTP request with patch method

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C#

ASP.NET

JSON

API

WebResponse

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Callback URL :

curl https://na1.Host.com/services/data/v20.0/sobjects/Account/ -H "Authorization: Bearer token -H "Content-Type: application/json" -d "@newaccount.json" -X PATCH 

Example request body newaccount.json file

{
"Name" : "Express Logistics and Transport"
}

I want to call web request using above callback url and data.

My code :

using (WebClient client = new WebClient())
{
     client.Headers.Add("Authorization", "Bearer " + token.access_token);
     client.Headers.Add("Content-Type", "application/json");
     NameValueCollection reqparm = new NameValueCollection();
     reqparm.Add("Name", "This Is Test Data");
     byte[] responsebytes = client.UploadValues(token.instance_url + "/services/data/v20.0/sobjects/Account/", "PATCH", reqparm);
     string responsebody = Encoding.UTF8.GetString(responsebytes);
}

Above code is not working. Getting Error (405) Method Not Allowed. I don't know how to use Patch Method.