How can i upgrade my pc?

I have been out of the pc game for a while, but now im looking to play again. Im wondering what the best way to upgrade my pc is with used parts. My goal is to be able to play newer games at 1080p, at or over 60fps without fps cuts. I would like to keep my budget at max 300usd, but i am also willing to sell parts from my current build to use more.

The pc has these specs:

-RX 5500-XT 8GB GPU

-AMD Ryzen 5 3600 CPU

-16GB DDR4 Ram

-2TB M.2 SSD, 256GB M.2 SSD, 2x 1TB HDD

-Unknown AM4 Motherboard

Thanks for the help!