title: Replace the child node in c#
body: <p>I have a string HTML code like </p>
  
  <pre><code> &lt;table id='topInfoBar' style=" width: 100%;" cellspacing='0' border='0'&gt;
   &lt;Tr&gt;
   &lt;td id='lockOrder' clientidmode='static'  style="text-align:Right;color:black;font-weight:bold"&gt;  
   &lt;img src='.../images/locked.gif' alt='This order is locked' title='This order is locked!' /&gt;
   &lt;/td&gt;
   &lt;/Tr&gt;
   &lt;/table&gt;
  </code></pre>
  
  <p>I want to check if id <strong>'lockOrder'</strong> exists in the string and if yes, want to replace img node i.e</p>
  
  <p><code>&lt;img src='.../images/locked.gif' alt='This order is locked' title='This order is locked!' /&gt;</code></p>
  
  <p>with </p>
  
  <pre><code> &lt;i class="fa fa-search fa-2x cursorpointer"  title="This order is locked"&gt;&lt;/i&gt;
  </code></pre>
  
  <p>want to do it in c#.</p>