As far as I know, there are two main folders created on your C: drive after installing FxSound:
C: \ Program Files \ FxSound LLC
C: \ Users \ [ your username ] \ AppData \ Roaming \ FxSound
The second folder will be hidden, so you’ll need to unhide it first if you want to delete it manually, by clicking on Tools > Folder Options > View in the menu bar on top, and enabling “Show hidden files, folders, and drives.”