Hi,
You can change Logo size in Module Manager via Logo module.

Plz go to Administrator -> Extensions -> Module Manager and select Logo module and
Replace
<p><a href="index.php"><img src="templates/ot_juno/images/logo.png" border="0" alt="logo" /></a></p>
By
<p><a href="index.php"><img border="0" width="200" height="100" alt="logo" src="templates/ot_juno/images/logo.png"></a></p>
Note: In IMG TAG, width="200" correspond 200px and if WIDTH and HEIGHT is null then size is automation follow size of IMAGE.