1. Go into your form editor if it is already on the page, select the entire form with the "blue" title at the top and then look for "edit" form button in your properties inspector... when you open the dialogue box for form builder, look for where it says "Choose a Design" and then you can select to edit from the blank design or any of the designed templates.
You'll then see a a drop down menu at the top - "form" will originally be selected, but you will want to choose "form elements" from that menu... then you will a second drop down menu below that containing all the possible elements you can edit... select "captcha" and then edit away. Make the captcha look however you want.
2. It is recommended to uninstall Validation Toolkit (previous versions) first because Form Builder has updated versions of the behaviors in Validation Toolit.