As Angela said, if you're wanting to un bold all of your field labels, you can do so easily under the Styles tab.

If you're wanting to isolate just one, you can use the following CSS:

#q73 label {
  font-weight: normal;
}

If you're wanting to isolate a few, but not the whole form, you can add a CSS class (in this case I used "unbold") to those fields and use the following:

.unbold label {
  font-weight: normal !important;
}