Question about upgrading my graphics card on a Dell XPS 8500?

Like the title says, I have a Dell XPS 8500 and I would like to upgrade my graphics card from the one I have right now (GT 640) to a GTX 950. I'm not really informative about how this works, since I heard that I'd maybe have to buy a better power supply or something in order to upgrade it, and also stuff like if it's compatible with my motherboard. Would I be able to just switch it out? If you need info about my computer specs I can check it if necessary.