Account and limits

In Settings. Deleting the account is permanent: it removes the account and every project in it, and there is no undo and no recovery window — so export anything you want to keep first.

Where

Settings → Delete account.

Cast asks you to confirm before it does anything, and the confirmation says exactly what will happen: the account and all projects go, irreversibly.

If the goal is to stop paying rather than to erase everything, cancel the subscription instead — you drop to the Free plan and your projects stay.