If it is before the renewal invoice has been created (30 days before expiry), simply go to https://register1.net/clientarea.php » Account Login » My Domains » 'view details' for the relevant domain, and click 'disable auto-renew'. No invoice will be created for the domain, and it will be left to expire. If it is after the invoice has been created please email dns@register1.net and confirm that you do not want the domain. We will then issue a credit for the invoice, and the domain will not be renewed.