Selecting the next element using HTML Agility Pack

I am using HTML Agility Pack and searching for div with class="fileHeader" that has "RelayClinical Patient Education with Animations Install zip" in a child h4 element. Once found, I want to capture the "href" attribute inside the anchor tag of that particular block. How can I get it?

HTML Source

<div class="fileHeader" id="fileHeader_7311111">
    <h4 class="collapsed">RelayClinical Patient Education with Animations Install zip</h4>
    <div class="defaultMethod">
        <a class="buttonGrey" href="https://mckc-esd.subscribenet.com/cgi-bin/download?rid=2511740931&amp;rp=DTM20130905162949MzcyODIwNjM0" title="Clicking this link will open a new window." rel="noreferrer">
            HTTPS Download
        </a>
    </div>
</div>

Code

HtmlNodeCollection fileHeaderNodes = bodyNode.SelectNodes("//div[@class='fileHeader']//h4");
foreach (HtmlNode fileHeader in fileHeaderNodes)
{
    if (fileHeader.InnerText.Trim() == "RelayClinical Patient Education with Animations Install zip")
    {
        HtmlNodeCollection fileHeaderNodes = bodyNode.SelectNodes("//div[@class='fileHeader']//h4");
        foreach (HtmlNode fileHeader in fileHeaderNodes)
        {
            if (fileHeader.InnerText.Trim() == "RelayClinical Patient Education with Animations Install zip")
            {
                foreach (HtmlNode link in fileHeader.SelectNodes("//a[@href]"))
                {
                    // extract the link and put in dataUrl var
                    if ((link.InnerText.Trim() == "HTTPS Download") && isFound == true)
                    {
                        count++;
                        // select all a tags (html anchor tags) that have a href attribute
                        HtmlAttribute att = link.Attributes["href"];
                        dataUrl = att.Value;
                    }
                }
            }
        }
    }
}