I think it sounds like you are referring to the "Unique Value" Field Heading that is showing up. But you can modify the appearance of both the actual Layer Name (how it is listed in the Table of Contents next to the check box) and the Heading (this is in the Table of Contents, but under the Layer Name) this way:
Right-click on your Legend and select Properties. From the Items Tab, select the appropriate Item on the right. Right-click on the Item you wish to modify and select Properties. On the General Tab, you can Uncheck Show Heading. If you click on the button Heading Symbol... you can modify the font, size, etc. instead.