It's always recommended to uninstall drivers and reinstall everytime an video card upgrade happens even if their from the same manufacturer and unified drivers architecture.
What is not necessary these days is to uninstall and reinstall every drivers update. The NVIDIA installer, for example, offers you the option to do a clean install
Btw, I have the same GTX 760 and I'm looking forward to do a budget upgrade to a GTX 970. Have you experienced a significant performance increase with this new video card?