I can't remember how I did it but I saw it in menu under file or picture size. Cant remember. It takes less megabites to load the pic though so I assume it uses less megapixels.
I'm guessing what your talking about is in the menu where you can choose file size. It's under image size in my D5000. I have a choise of small, med and large. If that relate's to changing the the pixel's, I never realized it. Tell you what, I shoot everything in large file, I can downsize in a photo program. I don't know that you could take photo in small size and take it up though. The only reason I could see to use med or small is to get more photo space in your card, more shot's without filling the card. At the large file size my camera's save enough photo's that I can simply change out for a different card. Now I'm guessing here but I doubt the small file will print as big a photo as the large file will. If you wanted to print one of the photo's at high file size, no problem. But the print the same photo at say 16x20, couldn't do it and get a good photo. But no matter which size you use I would think that each file size would make good print's but nit all at the same size. I got a photo in a week or so ago to frame for a friend. The photo was re-sized to made it easier to load on the internet, it would have could out a small size. Best size I could get with it was 5x7. Take the same photo and do it in large size and generally it'll blow up to 13x19+. So if I,m getting what your saying about 4mp, small size, or 8mp,Med or large size, the only difference you should see is in the size of a print you can make.
