A:Answer Yes, in fact you can replace anything inside the PC as long as you have compatible parts for them.
As for adding to it’s basic-components that it comes with, I recommend adding new RAM (4x 8GB DDR4-3200MHz), memory (hard drives/SSDs) and a CPU AIO (Liquid Cooler, and change out the power supply since it boasts a lowly 600W Gold Rating; I recommend at least 750W.
Changing any other M/B, GPU, CPU comes at your own risk and finding compatible components.