I've searched the web, but didn't find anything about way you can alter the payment methods and operations in MELO-D Merits. If you have the software installed, go to the Help section and read in the documentation section.
Alternatively, locate the installation directory of the software and look for CHM or PDF files. These are usually help files and user guides. You'll find much information in the user guide of an application. Secondly, access Help > About and note the contact options then send a direct inquiry to the developers, if they are still in the business.