Yes, you can upgrade your existing subscription directly in the shop. The remaining subscription period will be automatically credited to your new subscription after Teleboy Home is activated. The balance will be credited to your first invoice.
Please note that Teleboy subscriptions purchased as inApp via iTunes cannot be automatically cancelled by upgrading to Teleboy Home. These must be cancelled directly with Apple.
You can find help on how to cancel the inApp here: https://support.apple.com/de-de/HT202039