Setting the label text
CAPTCHA → Settings
Enter the text into the Label field.
CAPTCHA → Settings → Optional
You can choose whether you want the label above, left or inside the input. If you choose left, you will also be able to specify the width of the label to help control your form layout. The default value of Inherit means that the settings are inherited from the global form settings or the parent group.
Required indicator text
Settings → Style → Labels
Change the text indicating the element is required. By default this is (required), but you may want to make it an asterisk * for example.