Turn camera off, remove lense and use a blower bulb to blow out insides (don't actually insert the actual tip into the camera)..
Replace lens and take a picture of a blank wall at F22. This will give you an idea as to how much dust, if any, is left...
This site seems to be pretty comprehensive and reliable:http://www.cleaningdigitalcameras.com/..
Not a stupid question at all. Imagine trying to do it without finding out how first... and damaging the sensor. THAT would be stupid!.
The manual should have a section on how to expose the sensor so you can blow it clean (note: do not use the B setting to hold the shutter open as the sensor is still live, there is a separate setting for sensor cleaning which deactivates the sensor). A simple blower will work if the dust is loose, which it often is. Don't touch the surface of the sensor..
It happend couple times to me. I went to local camera store and asked your question there. They recomended sensor cleaning swabs and liquid. I used them 4 times during past year perfectly removing all dust specs from sensor and all lenses before shoting important events.http://www.stan-pustylnik.smugmug.com..
I use a brush fromhttp://www.visibledust.com.
The idea is you "charge" the brush (either with canned air or now via battery power) and then lightly wipe the brush over the sensor. then recharge the brush between swipes and afterwards. several swipes often gets the job done..
Apparently you can have substances (shutter grease?) on your sensor cover and that could require wet cleaning..
5D owners seem to be reporting that the sensor cover is easily damaged on that particular model..
If you shoot at f11 you will tend to see the spots more than if you are at f2.8.
For just a few spots you can use the healing brush in photoshop..