MyBB Community Forums

I would like my who's online to work like this:

1. Username
   
2. USername
   
3. USername
   
4. Username
   

<ol>
    <li>Username</li>
    <li>Username</li>
    <li>Username</li>
    <li>Username</li>
    <li>Username</li>
</ol>

How would I achieve this? What core edits does it require.