Hello Friend,
Look this:
After the demo content import you should have Popup transparent static Block (Dashboard > Static Blocks). Open the static block and find block id http://xstore.helpscoutdocs.com/article/47-static-blocks. Once you get it go to Theme Options > E-Commerce > Promo Popup and add the shortcode with your static block ID http://prntscr.com/eb6pe1
Form style:
http://xstore.helpscoutdocs.com/article/66-mailchimp-form-custom-styles
You need to edit your static block. You can to use Visual Composer editor, please, read documentation https://wpbakery.atlassian.net/wiki/display/VC/Visual+Composer+Pagebuilder+for+WordPress
https://wpbakery.atlassian.net/wiki/display/VC/Element+Design+Options
Regards