K.I.
Easy. Go to a nice jewelery store (not one in a mall) and start looking at diamonds, fun, fun! You can find one anywhere and take it to the place you bought your setting and have them mount it, or you can have the place you buy the diamond from mount it, easy!
Congrats and good choice!
I would have went with the bigger diamond too!
~I do not know about how much you will get for your old diamond but just a thought, do you have a daughter? I have decide if I ever get an upgrade I am going to put my original diamond in a piece of jewelery for my daughter for a special occasion, big birthday, college or HS graduation, first baby...who knows? But that way she will have a piece of her parents love with her, for forever and always!