Taking a look at the default MyBB theme, go to index_whosonline. You should find code resembling this:
Code:
<tr>
<td class="tcat"><span class="smalltext"><strong>{$lang->whos_online}</strong> [<a href="online.php">{$lang->complete_list}</a>]</span></td>
</tr>
<tr>
<td class="trow1"><span class="smalltext">{$lang->online_note}<br />{$onlinemembers}</span></td>
</tr>
Take a further look here:
Code:
<td class="trow1"><span class="smalltext">{$lang->online_note}<br />{$onlinemembers}</span></td>
{#lang->online_note}'s function is to show you this: 2 users active in the past 15 minutes (1 member, 0 of whom are invisible, and 1 guest).
{$onlinemembers}'s function is to show you which members are currently online.
Simply reverse the two functions in that line of code and it should look like this:
Code:
<td class="trow1"><span class="smalltext">{$onlinemembers}<br />{$lang->online_note}</span></td>
Save and refresh your forum, and your board stats for who's online should look like this: