i would recommend a new generation system, like a Ryzen 3 or 5 series and a modern discrete video card, not top of line, to fit your budget. i doubt you can upgrade your system without new mobo, ram, cpu at least.
what is your budget for upgrades? specify that and you will probably get lots of great responses
that cpu i referenced is an old AMD Athlon series cpu, was mentioned in the minimum specs.
PCPartPicker part list /
Price breakdown by merchant
CPU: AMD - Ryzen 5 2400G 3.6 GHz Quad-Core Processor ($157.99 @ SuperBiiz)
Motherboard: Gigabyte - B450M DS3H Micro ATX AM4 Motherboard ($54.99 @ Newegg)
Memory: Corsair - Vengeance LPX 16 GB (2 x 8 GB) DDR4-2400 Memory ($118.99 @ Amazon)
Storage: Samsung - 860 Evo 500 GB 2.5" Solid State Drive ($72.99 @ Amazon)
Storage: Seagate - Barracuda 2 TB 3.5" 7200RPM Internal Hard Drive ($57.99 @ Newegg Business)
Case: NZXT - H500 (Black) ATX Mid Tower Case ($64.99 @ Newegg)
Power Supply: EVGA - SuperNOVA G3 650 W 80+ Gold Certified Fully-Modular ATX Power Supply ($65.98 @ Newegg Business)
Total: $593.92
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-11-27 10:32 EST-0500
That has integrated graphics so medium settings in games, but, you can drop in a nice video card later and really play some modern stuff.