Which are the components that I need to upgrade for improved heavy demanding BR multiplayer games FPS ?

[Ronnie Pickering]

My rig is:
i5 4590 / 3,3Ghz / 6mb / LGA1150 / 4 cores
GTX 750 TI 2GB GDDR5
8 Gig of ram ddr 3 1600 mhz

Motherboard: GB B85M-D2V
Case CM CMP-350 500W

I cant upgrade CPU because it would cost me too much I only consider second hand GPU (because i found good deals on RX480 4G or RX 580 8G) or Ram or both.

Would an extra 8 gig stick help me ? ive seen threads some people say they got double the FPS with just an extra 8 gig stick when they had 8 but ive seen also alot of tests done that show only a negligible difference in alot of other places.

Also Do you think an RX480 4gig or RX 580 8 GIG would fix my issue in the games I want to play ? And If i do would it be beneficial for me to use both my old and the new RX at the same time?

The games that Im going for are Playerunknown's battlegrounds and Call of duty:Warzone. Pubg i can play but i do have alot of issues in it at times and COD:Warzone is just impossible even on the lowest settings.