I'm looking to get a better camera to move onto higher quality photos and options?

I'm looking to get a better camera to move onto higher quality photos and options for my small time photography business (portraits). Currently I have a Nikon D40. I would like to stay in the Nikon brand but open to any suggestions. Any help/advice would be appreciated!

If you really had a photographic business you would (a) know well that photo quality is down to the photographer not the camera and (b) you would, as a professional already know what equipment you needed.
Stop wasting our time please.