To cancel your Domain Subscription, from your Avatar menu on the top right, go to:
My Pro Account > Manage subscription
Under Domain Subscriptions, click Cancel Subscription
Note: For Studio and Plus accounts, it is the same process.
To turn off Auto-renew for your Domain subscription from your Domain admin:
Click your Avatar menu on the top right and go to:
Website Builder > Manage Domains > Manage > Auto-renew
Cancelling your subscription, or turning off Auto-renew, will not delete the domain from your ArtStation account. It will only prevent it from auto-renewing. You will still have access to the domain until it expires. Once it expires, your website domain will revert back to {username}.artstation.com.