Thanks for writing in. In taking a look at the form that's currently live on your website, it appears that you're using a different plugin, rather than the MailChimp List Subscribe Form.
Because the current form is not using this particular plugin, we're unable to provide Support on it, so your best bet would be to reach out to the developers of the specific plugin that you're using.
As a general recommendation however, I'd encourage using the "inspect element" tool that's available in browsers like Google Chrome. In using that, you can identify what CSS attributes need to be edited in order to control the design of your page's elements (like, making a certain piece of text larger).
Best of luck!