1. Uninstall the old version .
2. Install the new version .
Don't worry about old data . Nothing will be lost .
If you have modified the language file, please back up the language file first (language/en-GB/en-GB.com_pmform.ini) . After that, do the first two steps . The upload language file again to your server .
Just so you and others know. You do have to re enter your API and transaction key in the payments modules back-end after you upgrade. Thanks again Tuan!