The D50 is indeed 6 Megapixels - however, this doesn't mean the files are 6MB - they are actually closer to 15.5MB in their uncompressed form.
The JPG file is a compressed version of this 15MB file. Depending on the detail within the image, the files could be anywhere from 500k to 5MB, even at the lowest (finest) compression setting.
No need to change any settings.

but you might want to shoot in RAW format, which has a lossless compression and therefore even better image quality, a wider dynamic range and a smoother transition in fine tonal detail.