You can;t change or you change but there is no result?
ANYWAY TRY THIS:
You downlaod that mod. You don;t have to use it just 1 file from it. There are 3 folders called LOW, MID, HIGH settings hidden in a folder SETTINGS. You copy a file from folder and paste it in the GTA IV directory. It sets the quality in a game coz I think that useing ENB and icenhancers blocks options in a game.