The rules that apply are the rules of the last fare, so business. However any non refundable amount remains non refundable otherwise it would just be too easy to get any ticket fully refunded by upgrading to an higher refundable fare and then claiming a full refund. However the price difference between the non refundable (or partly refundable) fare and the business fare is then fully refundable. If you have a ticket at 50 EUR+tax and a 60 EUR refund fee, it makes it actually non refundable, just the taxes would be refunded. If you upgrade to business by paying 200 EUR extra, and then cancel, you would not lose 60 EUR (refund fee of the previous fare) but 50 EUR which is the amount you would have lost if you had cancelled the original ticket.