Are you playing at 1080p or a different resolution?
Likely, the CPU, motherboard and memory is where you need to start. There is nowhere for you to go as far as upgrades on that platform. It already has about the best CPU you can put into that platform, which was pretty weak even when it was new.
The least expensive upgrade option is likely moving up to a Ryzen 3, which would be miles better than what you have now.
This is about the least expensive upgrade that makes any sense at all. Upgrading your GPU card, with your currrent platform, still leaves it severely unbalanced as that 860k is going to bottleneck even a GTX 1050. This way, when you do eventually upgrade the GPU card, you will have a platform that can utilize it, plus you can eventually upgrade to a much higher performance CPU on this platform and add another 8GB of RAM for a total of 16GB at some point. Even if you don't do either of those things, this would still get you a lot closer to where you want to be if you upgrade the GPU at some point, and for use with the GPU card you already have in the meantime.
PCPartPicker part list /
Price breakdown by merchant
CPU: AMD - Ryzen 3 2200G 3.5GHz Quad-Core Processor ($98.89 @ Amazon)
Motherboard: ASRock - B450 Pro4 ATX AM4 Motherboard ($69.99 @ Newegg)
Memory: G.Skill - Ripjaws V Series 8GB (2 x 4GB) DDR4-2666 Memory ($69.99 @ Newegg)
Total: $238.87
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-09-14 14:34 EDT-0400