recommendations on what to with hand me down pc

[u/Savings_Analysis_753]

Ive been playing on this hand me down pc that ive gotten from a relative for about a month now and because its my only pc and I want to play better games on it what should I do with it sinceI have been playing game that can run fairly easy such as minecraft, roblox, valorant. The only problem is that I want to play games like CS2 or Fortnite without being at 90 fps so im confused if somethings wrong with my setup, I need to upgrade it or I should just build an entirely new one.

CPU:Intel i5-8600k

GPU:RX 580 8gb

Motherboard:Gigabyte Z370 HD3P

CPU Cooler: be quiet! Pure Loop 120 Liquid CPU Cooler

Memory: TeamGroup (2 x 16) DDR4-3600 CL18 Memory

Power Supply: EVGA 850 W 80+ Bronze Semi-Modular Power supply

Please let me know on what to do that would be very helpful.