if you are a user, then you wont be able to, you need to be admin. check your userclass status in your database user table.once your set to admin, you should see a link to adminpanel
if you are admin, then simply go to here
your_site.com/admin
if you look inside templates/header.php and open with say notepadd++ you will see a part of code
Code:
<? if (is_logged_in()) { ?>
<? if ($_SESSION['privilege'] == "admin") { ?>
<a href="<?=$CFG->wwwroot?>/admin"> <img src="<?=$CFG->imagedir?>/admin.png" width="70" height="40" border="0"></a>
<a href="<?=$CFG->wwwroot?>/update_stats.php"> <img src="<?=$CFG->imagedir?>/updatestats.png" width="110" height="40" border="0"></a>
<? } ?>
if admin then you will see 2 links in header, Admin, and update stats.. you see how it points to /admin (your admin panel)