Please don't take offence, but the d700 is a professional camera designed for people who know what they are doing and have a grounded knowledge of photography.
Judging by your previous posts, and by your own admission, you are very much a Beginner.
Now there is nothing wrong with owning the best gear you can, but I highly suggest you spend time learning everything about the d700, and everything about photography before even considering upgrading.
I can assure you, at this point in time, any issues you may be having with image quality are purely down to your inexperience and not the camera lacking in any way.
I've owned a d700 for about 4 years and there are still some aspects of it I haven't fully got to grips with.
Upgrading won't make your photos any better, the d700 is more than adequate for anyone who doesn't need specialist equipment for their full time profession. You just need to learn how to utilise its huge array of features.