Best answer I can give is to sell your current PC.
The upgrade path for gaming is no longer economical and effective.
Let me say it another way. If you said 'software upgrade', you would have lots of options. If you had said 'beautiful hardware' you also would get answer. But you asked for hardware that would up your FPS.
It's not economical. There is no economical hardware upgrade to improve FPS in a significant way.
Thais not my idea.
Most of the time life hacker is right on. Look at this:
https://lifehacker.com/how-do-i-know-when-to-upgrade-my-pc-or-just-build-a-new-1571878154Sometimes it can feel like your best bet is to just build a new computer entirely ..
He goes one to examine some things your need to know about what new hardware is out there.