Without a URL, I'll just guess this one out as is. That heading is controlled by the LABEL. You can fix it two ways.
One method is to do it properly;
http://www.zen-cart.com/forum/showthread.php?t=46098
The second method, you can fudge it out in your stylesheet.css;
Find;
LABEL, h4.optionName {
line-height: 1.5em;
padding: 0.2em;
}
Replace with;
h4.optionName {
line-height: 1.5em;
padding: 0.2em;
}
LABEL { font-size: 1em;
line-height: 1.1em;
padding: 0.2em;
}
And find;
h4, h5, h6, LABEL, h4.optionName, LEGEND, ADDRESS, .sideBoxContent, .larger{
font-size: 1.1em;
}
Remove the red portion.
Like I said, I'm guessing on the version of Zen Cart that you have. These modifications are for 1.3.5, but might work for others. As you can see, there is a bit of work to do both ways.