It will happen to you some day. You’ll be shooting pictures or video and notice a smudge, spot or smear on your pictures, particularly after running color correction. Don’t panic, it happens to everyone at some point in their photography career.
There are two basic ways of dealing with a dirty sensor: Shipping it off to a service center to have it done professionally, or doing it yourself.
If your camera is still under warranty, then sending it off would be the default option. If not, then you might consider doing it yourself. I’ve had cameras come back from the service center just as dirty as when I sent them in. Once the spec on the sensor was still there, I don’t think they even looked at it. If you’re careful and patient, you can do it safely on your own.
The Copper Hill Method
Copperhillimages.com Carries cleaning kits sized specifically for different camera models. There are a couple things you will want to get besides the basic kit.
Your best bet is to get the Mega-Kit which wasn’t offered when I ordered mine. For sure get the Sensor View magnifier or pick up a lighted magnifier somewhere else. That makes working in the dark insides of your SLR a lot easier.
The other component you’ll definitely need is the SensorSweep brush or similar static brush. I’ve never seen fibers cling for desperate life like they do inside the sensor chamber. It’s like they’re glued on sometimes.
Don’t use any kind of metal tools inside your sensor chamber unless you really know what you’re doing.
Copper Hill has detailed, step-by-step instructions for sensor cleaning. I would advise going through the tutorials carefully and lay your cleaning supplies out in advance.
A dirty sensor isn’t the end of the world, but if you scratch the sensor, it’ll be the end of your camera. Be patient, careful, and gentle and you’ll be fine.