Upgrading diamonds

Has anyone ever upgraded their diamond, either a different color or clarity or size? Just out of curiousity...I love my ring and would never change it.
Do you trade in your diamond for another one and pay the difference or do you have to buy a new diamond?
If you trade it in do you get what the diamond is worth or they won't give you that much money?

Any reputable diamond dealer will take the stone back and pay you what you paid for the diamond (they appreciate in value so they are still making money on the deal)

They should put that towards a new diamond which would presumably cost more.

Think about it - they can resell the diamond for the same price (actually more) and they get you back into their store to spend more money. Why wouldn't they take it back?

You won't get as good of a deal if you sell it one place and buy somewhere else though