Thanks for posting! In taking a look at the screenshots you provided, I'm seeing some indication that perhaps a different plugin is being used. To confirm this, can you login to your WP-admin area and go to the Plugins page, then confirm for me what the title of the active plugin says, as well as what version you're running? To ensure we can provide the most accurate help, please make sure that this plugin is up-to-date (version 1.2.14).
With our plugin, the label of the form field is controlled by what's setup in your MailChimp account, so changing the displayed name for the field can be done by going to your MailChimp account's list settings and changing that there. If you're already made the change in your MailChimp account (and can confirm that it's showing with the desired field label when you view your MailChimp-hosted sign up form), then the last step would be to make sure your plugin settings are updated. To do this, log in to your WP-admin area, then go to Settings > MailChimp Setup, and click on the "update list" button at the top. This should ensure the form field labels are up-to-date.
If you have any questions, let us know!