How do I manually delete a cookie in asp.net MVC 4

Try:

if (Request.Cookies["MyCookie"] != null)
{
    var c = new HttpCookie("MyCookie")
    {
        Expires = DateTime.Now.AddDays(-1)
    };
    Response.Cookies.Add(c);
}

More information on MSDN.

c.Expires = DateTime.Now.AddDays(-1); This does not clear cookies instantly.

Use this: c.Expires = DateTime.Now.AddSeconds(1); This will clear cookies instantly.