It doesn't improve performance, you actually loose relative performance as DLSS 4 takes more GPU power to run than DLSS 3. Sure you will get higher FPS than when DLSS is turned off, but less relative to DLSS 3.
The picture quality is somewhat better, but not much and not really noticeable, I've concluded after using DLSS 4 in Planet Coaster 2 for the last month. Some games hand themselves well to DLSS, others not so much.
You can upgrade DLSS yourself, on Planet Coaster 2 or any game for that matter by using the handy DLSS Swapper tool. (Google it). It takes 5 seconds to swap out the DLSS.
