Need Help: Removing program from disk

Guys...need your assistance to share your knowledge on how to remove program installed in macbook disk.

I just installed a trial version of DPS Plug-in v.1.2. Now I want to install the program with the older version - 1.1. When installing it the notification appeared inform that the newer version of Digital Power Station has been installed. Actually, I have used the uninstaller provided by v.1.2. and seems it doesn't work.

Any idea to sort out this matter? Thanks and much appreciated.