Upgrading FS9 to FSX or replacement?

It has been rumoured that my Grandsons are considering FSX for my Christmas stocking. (I presently have FS9 and the 3 CFS's to keep my retirement days occupied.) However, I have done some serious upgrading to FS9 both in scenery and aircraft over the past months. Is there a method/program that upgrades FS9 to FSX, or do I have to install FSX, and compare to FS9 to determine what aircraft/scenery upgrades are necessary to bring FSX at least up to the present level of my FS9? And is FSX so much better than FS9 that I want to go through some extensive "renovations"? If I do replace FS9 with FSX, should I uninstall FS9? :-/