You can update both your shipping and billing addresses through your Huel account.
To update your shipping address (for subscriptions):
Log into your Huel account
Click on My Subscriptions
Select Manage Subscription
Below the price of your upcoming order, find the Shipping section
Click the Edit button next to it
Make your changes and click Save
To update your billing address:
Log into your Huel account
Go to Payment Methods
Click Edit on the card or payment option
Enter your new billing address and click Save