To reinstall or update DITA-FMx over an existing installation, just run the installer. No backup or uninstall is required. The installer will overwrite all like-named files in the DITA-FMx folder. It will not overwrite the ditafmx.ini file, so your settings will not be lost.
If you’d like to get a “fresh” install, you can rename the existing DITA-FMx folder (perhaps to something like DITA-FMx.<oldversion>) before running the new installer. This will give you a completely new installation of files, but will let you compare the new files to the old files and allow you to “roll back” to a previous version if needed. If you choose this approach, you will need to manually migrate any manually entered settings in the ditafmx.ini file.
After reinstalling, you may want to copy the new structure applications to the FrameMaker\Structure\xml\ folder so you can take advantage of any changes that have been made.
Proceed to Run the Installer Application.