How to change currency to other than USD?

Hi there,

How can I change the currency of service price in Appointments+? Currently the price is displayed in USD. I want to change it into PLN (Polish Zloty). Following suggestions from this thread
I found the 'currency' line in code within 'appointments.php' file (around line 4240) and changed it to 'PLN'. Unfortunately that didn't help.

Cheers,
Tomek