as long the dust is not on the sensor, don't bother too much about it. it won't show up on the images.
the sliver coating on the reflex mirror is at the front, easily scratched if you touch it with anything.
the matte surface of the focusing screen is facing downward (facing the mirror), it is also very easily scratched if you use anything to clean it.
so just blow it with blower, if the dust still there, leave it, don't risk your camera for damaging the reflex mirror and focusing screen.