How can I change the font size in the logo module text.?

Hi there,
therefore you have to edit the source code of the logo module:
>> Disable the Joomla Editor and look to the HTML code of the module:

<div style="margin:50px auto;width:500px" data-uk-scrollspy="{cls:'uk-animation-slide-top'}" class="uk-scrollspy-init-inview uk-scrollspy-inview uk-animation-slide-top">
<h1 style="font-size:80px;color:#000;font-weight:100">SOUNDS</h1>
<h2 style="font-size:17px;line-height:17px">DESIGNED &amp; PRODUCED IN GERMANY</h2>
<i class="uk-icon-headphones" style="font-size:50px"></i>
<h3 style="font-size:16px">In a world demanding rich communications anywhere any time on any device, our products enable voice, messaging, IP multimedia services and business</h3>
</div>

Problem solved.