Desktop Hardware and Upgrade Questions

Hello, new to computer building/upgrading so sorry for the basic questions I am still trying to learn and figure this out but it's not very clear. I am looking at trying to upgrade my graphics card, hard drives, and RAM but having a hard time understanding what I can use. Some of the specs are listed below that show installed currently. 

I want to either add a new graphics card or replace this with a better one but not sure which one applies. Do I replace it or can I add to it? What should I be looking for when doing this? Do I need to upgrade the power source as well? The main goal is to play computer games. The main game I have right now, but can't play because of the graphics card, is COD warzone.

Also, I want to add storage, but again, am unsure if I am supposed to replace what I have or if I can just add to it? What should I be looking for?

Finally, I intend to get another 16gb RAM stick with the same information as the one listed to boost it to 32gb. But is that all that I can install? I am pretty sure there are only 2 RAM slots, but am I able to get 2 32gb sticks to go to 64gb total? I don't understand what the limiting factor would be here and just want to make sure everything works. What is the maximum that I can put in the computer?

Any information anyone could provide would be greatly appreciated. Or is someone could even point me in the right direction. I don't mind researching and finding out the answer to learn but I am confused about it all currently.