That prebuilt sucks.
I'm just going to assume your budget is ~$800.
PCPartPicker Part List:
https://pcpartpicker.com/list/GQfg4nCPU: AMD Ryzen 5 3600 3.6 GHz 6-Core Processor ($172.99 @ Amazon)
Motherboard: Gigabyte X570 GAMING X ATX AM4 Motherboard ($159.00 @ B&H)
Memory: G.Skill Ripjaws V Series 8 GB (2 x 4 GB) DDR4-3200 Memory ($47.99 @ Newegg)
Storage: Silicon Power A80 1 TB M.2-2280 NVME Solid State Drive ($129.99 @ Amazon)
Video Card: Gigabyte GeForce GTX 1650 SUPER 4 GB OC Video Card ($159.99 @ B&H)
Case: NZXT H510 ATX Mid Tower Case ($69.98 @ Amazon)
Power Supply: EVGA B5 550 W 80+ Bronze Certified Fully Modular ATX Power Supply ($66.98 @ Newegg)
Total: $806.92
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2020-04-23 18:03 EDT-0400