Changes/Enhancements to Existing PHP Project/Plugin

We have a website created using GeoCore Plugin that is purchased from [login to view URL] We need few modifications in the website that we have created using the above plugin e.g. adding new fields while creating the classifieds, saving those fields into the database and displaying those new fields into the database. Also need few changes in the payment flow. This software/plugin uses a standardized PHP Framework, so only person with experienced PHP is required.