I have the D50 and I use it mostly in the outdoors, getting a little bit dirty although I try hard to keep the dirt away from it. I also ride with it in my backpack a lot. I've had it for about a year and a half and it has been great, but now I am seeing spots showing up in my photos, always in the same places, and it doesnt matter what lens I use (so it's not something on the lens). I can see some stuff there when I look through the viewfinder. I cleaned the mirror inside the body but that didn't do much, and also around the viewfinder on the inside of the camera. I think it's time that I give my camera, probably the sensor, a good cleaning to get ready for the busy summer season. Can someone tell me how to go about doing this, tips, or what I should do? Something I can do myself or not? (I prefer to do things myself when I can)

As an example, you can see a few spots in the upper right section of this photo I took a few days ago:


Thanks.