Depends how much money you want to spend. Upgrading from that CPU will likely require a new motherboard, which might benefit from new RAM, too. That's a hefty chunk of cash if you do it properly. A new GPU could be had for less than those three, but if your CPU is the bottleneck, it won't matter a huge amount.

I'd suggest monitoring CPU usage while running the Stormblood benchmark (something like OpenHardwareMonitor works well). Check if any of your individual cores are being fully utilized. Similarly, monitor your graphics card. One of them is likely being pushed to its limits; whichever one is, that's your bottleneck, and that's the one that should be upgraded.