using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string input =

@"<div class=""tr-summaryinfo"">

<p class=""tr-summaryitem"">test </>

</div>";

​

        string result = Regex.Replace(input, "<div class=\"tr-summaryinfo\">(.*?)</div>", "<ul class=\"tr-summaryinfo\">$1</ul>",

            RegexOptions.Singleline);

​

        result = Regex.Replace(result, "<p class=\"tr-summaryitem\">(.*?)</p>", "<li class=\"tr-summaryitem\">$1</li>",

            RegexOptions.Singleline);

​

        Console.WriteLine(result);

    }

}