In your Auctiva account, click on the "Profiles" tab. Click "Manage Seller Details" in the Seller Details section. Choose the Seller Details profile that you want to edit (you probably only have one) and click Edit. Once the page loads, click where it says "Switch to Standard". The editor will load, and by clicking on any of the tabs across the top you can change the font size and style for any section of the Seller Details.