How about this code snippet? Your query is a general query. if you are specific about something then you may expect a better answer.
CookieContainer cookieJar = new CookieContainer();
CookieCollection cCol=cookieJar.GetCookies(Request.Url);
foreach (Cookie cookie in cCol)
{
if (cookie.Name == "myCookie")
{
cookie.Value = "100";
Response.Cookies.Add(new HttpCookie(cookie.Name,cookie.Value));
}
}