What should I replace on my gaming PC??

[Mistak4n]

Hey there guys, after about 3 years of no hardware upgrade I am starting to look into what I should prioritize considering the parts I already own.
Here is my rig right now:
Processor: Intel(R) Core(TM) i5-4590 CPU @ 3.30GHz 4 Cores
Video Card: NVIDIA GeForce GTX 970
Ram: Kingston 8(2X4 GB) DDR3
Motherboard: ASUSTeK Computer H97-PLUS
SSD: kingston sv300s37a120g
HDD: Samsung HD520IJ
My main goal is to play 1080p at max settings with at least 60 fps and i have a 400 dollar budget right now, I thank everyone for any help given.

 

[KR2]

Possibly get 8GB more RAM to get 16GB which will benefit you quite a lot since games coming out these days are becoming increasingly demanding on RAM. I would also consider upgrading the GPU and getting a GTX 1060 6GB since it has 2.5GB more VRAM and also outperforms the GTX 970 in every way.

 

[geofelt]

You have a nice and reasonably well balanced pc.
$400 budget will allow you to upgrade cpu or gpu, but not both.

Some games are graphics limited like fast action shooters.
Others are cpu core speed limited like strategy, sims, and mmo.
Multiplayer with many participants tend to like many threads.

You need to find out which.
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To help clarify your CPU/GPU options, run these two tests:

a) Run YOUR games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
If your FPS stays the same, you are likely more cpu limited.

b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 80%.
Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
This will simulate what a lack of cpu power will do.
Conversely what a 20% improvement in core speed might do.

On graphics, you are looking at possibly GTX1070; anything less will not be an impressive upgrade.

On cpu, If you will buy used, I7-4790K and a Z97 motherboard would be a reasonable upgrade.
But... I5-7600K, Z270 motherboard and DDR4 is really the way to go.