There is no special functional. You have to order new Linux VPS, and refuse from Windows VPS. At that all Windows data will be deleted. You have to download your data to Linux again.
You follow all the steps as before via idhost.kz But on the last step, you choose “I’m already a client”, enter your login and password, and order is added to existing accounting.
You have to place an order for canceling. Enter Billing section. Then go to section My subscriptions or Subscription Management Press name of Subscription plan then press button Cancel subscription in the field “Comment *” indicate the reason of canceling. Now press the button in the right bottom Cancel subscription. You are succeeded. Service promptly shifts to mode Stopped. As administrator considers your order, money for not wasted period will be returned to your balance, and service will go to status canceled /deleted.