To add another adult to your existing group/family membership please follow these instructions
From the home page (shot 1) choose the members pages menu item.
The top option will be Members Login page (shot 2).
Here you fill in your username (or email address) and password and you go to the members landing page (shot 3). Click on update your membership and details.
Shot 4 shows all your details. Click on the option to renew your membership. That takes you to a stripe page where you type in your credit card details and you will be done!
Shot 5 shows the message you get when you succeed!