Pc tweaking on a very LOW end pc.

Hi guys so i have a

Dell optiplex 3020 MT

i5 4590 4 cores 4 threads

msi ventus ox gtx 1650 Desktop model

16 gb of ddr 1600mhz (supports 2133mhz)

I play fortnite but i can mostly have around 80-140 fps

i play on performance and some potato graphics but sometimes i get some huge fps drops or stutters

also my cpu all cores are at 89-100% while my gpu is at 25-30%

when playing only 9gbs of my ram is used
Any tips on how to fix these stutter?

also please dont say get a new pc i dont have the money for it right now...