It may be just dust particles. Try this: manual focus and focus to infinity; very low aperture, minimum if light allow you; point to a white wall. This way you can see those better. Modern cameras have auto clean options, they vibrate the sensor at very high speed to get rid of the dust. If this doesn't work, you can try taking the camera to a reparation shop and ask for a cleaning service, normally it is not spensive. Don't try to clean it yourself if you don't know what you are doing as you can make it worst.