From what I can ascertain, it's as easy as downloading the installer and doing the setup process. PhotoFiltre Studio
Decompress the archive and then open pfs-Setup.

To my understanding, photofiltre7 is the free version whereas photofiltreX requires a purchased license.

Are you sure you actually deleted the photofiltre7 application or only the shortcut?
Check your applications for photofiltre and/or do a system-wide search for it.