When you see crud in your pictures, the stuff is either on the lens or, most likely, sensor.
Cleaning the sensor starts with putting the camera in "manual cleaning" mode with a fresh battery, which locks up the mirror, and carefully blowing air at the exposed sensor with a bulb blower. Anything after that could void your warranty under Canon's policies. ["After that" includes a dry cleaning with a sensor brush or pad, then a wet cleaning with methanol dampened wipes].
For a camera under warranty most folks would send it in to Canon if the air blower cleaning was unsuccessful. That said, sensor cleaning, when done following the guidelines recommended by manufacturers such as Dust-Aid, VisibleDust, and Photographic Solutions, is pretty straightforward stuff.