Dear Tedd,
You can try to do this, but most likely that you will need to make changes in php files again. Probably css files you can copy from free version, but php files need to be edited manually.
Follow this tutorial while upgrading and don't forget backup files:
ordasoft.com/News/Real-Estate-Manager-Do...thout-lost-data.html
Best Regards,
Anna
ordasoft.com