Inserting a new value in an HTML structure

Inserting a new value in an HTML structure

For example I have an HTML file like this

  1. <td id="td_id">
     <h1 class="h1_class">
      <a href="testme.com">Title</a>: Sub-title
     </h1>
    </td>

The output of this would be "Title: Sub-title"

But what I need is to insert a new value using jQuery so that the value would be

"Title: New Value Sub-title"

I can't insert a value in between the comma and the word sub-title.

I tried using the td's ID and moving down to it's child but I can't seem to add a value.