Question Not sure what things I should change in my PC

Oct 5, 2020
So, I've been thinking about changing up some stuff in my PC since it is already 8 years old and, while it can still run most games I play and stream just fine(not always in 60FPS), I want better performance in more recent games. Plus, I'm kinda scared that my computer is overheating(it never turned off or anything, but it gets REALLY hot aaand my city is currently 38º and realy dusty).
Given that, I thought about changing the CPU + Motherboard + RAM, but this would really hurt my wallet(given that I live in Brazil and prices have skyrocketed since March). The other option I thought was just getting some better DDR3 RAM, but I don't know if it would be worth it. What do you think would be the wisest thing to do? My budget would be something close to U$400 dollars. Thanks in advance guys :)

CPU: Intel Core i5 2500K
GPU: EVGA GTX 960 SuperSC 4Gb
Motherboard: ASUS P8H61
RAM: 8Gb DDR3 667MHz
Storage: 2x Samsung 1TB HD103SJ + 120Gb SSD Kingston SV300S37A120G
Power Supply: Cooler Master Bronze 600W (I don't know the model sorry)
Some games are graphics limited like fast action shooters.
Others are cpu core speed limited like strategy, sims, and mmo.
Try this simple test:
Run YOUR games, but lower your resolution and eye candy.
This makes the graphics card loaf a bit.
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.

Run Hwmonitor.
It will tell you current, min amd max temperatures.
If you see a max of 100c. it indicates that your processor has throttled and lost performance.
At idle, you should see 10-15c. over ambient if your cooler is mounted well and is functioning.

What is your budget? A moot point to me since I do not know your shopping sources.

If you can handle, better graphics, look at a GTX16xx class card or better.
While your psu is not the best, it should be able to run any graphics upgrade you might want.

If you are cpu limited, that is tougher.
A Z motherboard would allow you to overclock the K for some 20% better performance.
A i7-3770K would be the strongest processor that your motherboard would support.
Perhaps $110 used on ebay in the US.
Here is a list of supported processors for your motherboard:

Ram speed is not important to intel. 667 is fine.
The important thing is to have enough.
Look at task manager memory tab. If the hard fault page rate is zero you have sufficient ram.
Otherwise, buy a 2 x 8gb ram kit.