A few things. You cannot replace the admin with an active guest account. First, you'd need to remove the guest, then replace the admin with it.
Now, since the subscription is linked to the current admin account, and the store cannot be updated, you will not be able to replace the admin until the active subscription expires. If you remove the admin account now, you will no longer be able to manage the subscription in the future. One alternative is to cancel the subscription, then create a subscription case and provide the new admin email address and we will update the admin account for you, from our end: Subscriptions – Hubitat Support
