You have an entry-level GPU for 1080p gaming and a very very weak CPU. Between the two, I'd upgrade the CPU first.
However, the dilemma is, the FX CPUs are already a dead-end upgrade path. IMO, you'd not be spending your money wisely if you buy a new CPU of the same platform. The only advantage of getting such CPU is you get to retain the same motherboard and RAM you currently have (not spending more).
If I was in your position, I'd change the CPU + MB + RAM to either an AMD Ryzen 5 or an Intel Pentium/i3/i5 platform (the choice of which is dependent on your budget). However, compared to the first option above, this would have a higher overall cost than just changing the CPU alone. But the CPU + MB + RAM upgrade will give you the opportunity to upgrade to more powerful components in the future, unlike in the first option where you'll be stuck at the FX build with a weak GPU. In the CPU + MB + RAM option, you can get the best CPU you can afford and upgrade your GTX 950 at a much later time to a more powerful one without any bottlenecking - which is what you might be experiencing now with low fps (https://docs.google.com/spreadsheets/d/14LcYGkqVqaHUK_qwS_6N9s1vp-TH7AyHzn7OrNittag/edit#gid=0).