Where can I change/update my card details?

To update the payment details of your Dux-Soup subscription, log in to your Dux-Soup account via https://app.dux-soup.com/web/profile .

Then, go to "Manage Account & Subscription".

Here, click on your Dux-Soup Subscription 

Click "Payment Methods".

Now you will be able to update the credit card details.