[Theme: Zenon Lite] Text Size

In your style.css or custom style box, you could change the following code, which appears on line 16, according to the preview:

{
font-family: 'YanoneKaffeesatzRegular';
letter-spacing: 0.05em;
font-weight: normal!important;
}

You can change the font-family to Arial. Then you could write:

h1 a {
font-size: ?px;
}

Just fill in the question mark with whatever size you want.

Go to Appearance> Editor and select “Stylesheet” from right and add this line to the very bottom:

body #topmenu ul li a{font-size:18px!important;}

Ah yes, my example was from misreading your question as “the text on top of the menu,” thanks @tislam100 for noticing that.