Welcome to the site. And I agree, a fantastic site and community here.
There are a few ways to remove a card. From the add/update view, you can select "remove" from the dropdown next to the individual card.
Or, from the "choose an action" dropdown, you can "remove all cards from collection". This will only remove all cards in the current context (i.e. the set you are in, not every card in your collection, in this case).
It's worth reading the faq found in the footer of each page to get many good hints and tips.
Good luck and don't hesitate to reach out if you have any questions.