Update a user profile in Yammer with a PUT request. Could be improved by using the newer HttpClient library.

update.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            const int userId = 5189753;
            const string accessToken = "";

            // N.B. Use something other than a dictionary to support passing
            // education[] multiple on the query string. This will error
            // with duplicate key warning.
            var propertiesToUpdate = new Dictionary<string, string>
            {
                {"full_name", "This is a new full_name"},
                {"job_title", "This is a new job_title"},
                {"location", "This is a new location"},
                {"mobile_telephone", "This is a new mobile_telephone"},
                {"work_extension", "This is a new work_extension"},
                {"significant_other", "This is a new significant_other"},
                {"interests", "This is a new interests value"},
                {"summary", "This is a new summary value"},
                {"expertise", "This is a new expertise value"},
                {"work_telephone", "0118 999 881 999 119 7253"},
                {"department_name", "New dept. name"},
                {"education[]", "UCLA,BS,Economics,1998,2002"}, // undergraduate only
                {"previous_companies[]", "Geni.com,Engineer,Building desktop apps,2005,2008"}, // first only
            };

            UpdateUser(userId, accessToken, propertiesToUpdate);
        }

        private static void UpdateUser(int userId, string accessToken, Dictionary<string, string> newProperties)
        {
            var userUrl = CreateUserApiUrl(userId);
            var requestParameters = CreateRequestParameters(newProperties);

            // PUT https://www.yammer.com/api/v1/users/9123456.json?work_telephone=123456&department_name=deptname HTTP/1.1
            var putRequestUrl = string.Format("{0}?{1}", userUrl, requestParameters);

            var putRequest = (HttpWebRequest)HttpWebRequest.Create(putRequestUrl);

            putRequest.Method = "PUT";
            putRequest.Headers.Add("Authorization", string.Format("Bearer {0}", accessToken));

            string result;
            var putResponse = (HttpWebResponse)putRequest.GetResponse();
            
            using (var rdr = new StreamReader(putResponse.GetResponseStream()))
            {
                result = rdr.ReadToEnd();
            }
        }

        private static string CreateRequestParameters(Dictionary<string, string> newProperties)
        {
            var body = "";

            foreach (KeyValuePair<string, string> item in newProperties)
            {
                body += string.Format("{0}={1}&", item.Key, item.Value);
            }

            return body;
        }

        private static Uri CreateUserApiUrl(int userId)
        {
            return new Uri(string.Format("https://www.yammer.com/api/v1/users/{0}.json", userId));
        }
    }
}