There is nothing else worth upgrading. If you want to upgrade completely, you can only change the whole set, except the monitor. The hard disk only has IDE port, so there is no need to keep it.
Either add memory and continue to make do. Anyway, lz also said that it doesn't need to be too extravagant, which means that it can make do at present; Or change the entire setting:
CPU Intel G620 boxed CPU (LGA1155/2.6 GHz/3M3 cache) ¥4 19.
Motherboard ASUS P8H6 1-M LE Motherboard (Intel H61/LGA1155) ¥ 459.
Memory south Asia Yisheng DDR3 1333 4G desktop memory 1 19
Hard disk western data WD 5000AAKX 500G7200rpm 16M SATA III 6GB/s 3.5 inch desktop hard disk $599
CD-ROM drive Lite 18X series DVD drive black 92
In addition, the power supply of the chassis does not exceed 2000, which is much smoother than the current configuration.