I am not sure it was a "free" change. The overall price of the holiday has now risen by £63 making the balance payable increase. Fair enough, the price of the flights might have increased, but when I received the email confirmation it showed :
Charges/Admin: £25.00
Total New Payment: £350.00
Payment date: 27 Apr 2020
So, it is possible that the overall £63 increase includes some element of a charge but hat is not broken down and therefore not clear.