You can change blur and depth of field settings inside "icenhancer_config.txt"
in your GTA IV main folder after installation.

You have to change the number after "#define MOTION_BLUR" to change blur.

If you want to enable/disable depth of field put the number 0 (off) or 1 (on) after "#define DEPTHOFFIELD".

I would recommend to leave other changeable settings how they are.