The Cohhilition

I recently traded someone for their gaming PC and compared to my old one (that was not really a gaming PC this thing is a monster)
I know it is prob weak as hell compared to all of yours but I could use some insight and so on.

This is what I know about it from what I pulled off the computer:

Processor: AMD FX(tm) 8120 Eight-Core Processor 3.11GHz
Ram: 16GB
System Type: 64 Bit operating system, x64 based processor

Card name: AMD Radeon R9 200 / HD 7900 Series Manufacturer:
Advanced Micro Devices, Inc.
Chip type: AMD Radeon Graphics Processor (0x6798)
DAC type: Internal DAC(400MHz)
Graphics Card Manufacturer - Powered by AMD Graphics Chipset AMD Radeon R9 200 / HD 7900 Series
Memory Size - 3072 MB
Memory Type - GDDR5
Memory Clock - 1425 MHz Core Clock - 1000 MHz
Total Memory Bandwidth - 273 GByte/s Memory

Questions are what should I slowly start doign to upgrade so i can play games on the highest rezolutiona nd so on......
(I am playing Overwatch on Medium to get about 140 FPS right now -_-)

I want to play Rainbow Six Siege on here but I am afraid I'll lag like crazy and not get the FPS I need to even compete.....

Any help and advice is appreciated

thanks

Upgrade your graphics card and you'll be good for a while. Processor isn't bad, and RAM is plenty. SSD can always help if you don't have one, but that's not priority.

Any ideas on a card?
What am I looking at for cost?

Could I run R6S with that new card well?

Im comp stupid and know nothing about what does what for a pc?

If you have the money buy a new rig intel i5 processors and Nvidia 1060 will do nicely if you are on a budget I suggest Ryzen 5 CPU and RX 550 card. Look here http://www.logicalincrements.com/ and here https://www.passmark.com/index.html