I have a 1.5 ct ring that has a gold band. Wifey wants it changed to a platinum or white gold ring but the same exact design that it is in now. does zales or these other diamond stores do that for you? or is it some kind of private sellers do it?
It won't be an even swap, you can't just turn in a used setting and get a new one, but if the setting is still being made it's probably best to go to where it came from and see if they do it in white gold or platinum. They should also be able to give you credit for your old gold setting. If they can't help, please post a photo here and we can try to find the setting for you!
have you considered having your current yellow gold setting rhodium plated? so it'll look white gold colored. it doesn't last forever but several coatings over the years may be cheaper than a whole new setting.