I'm not sure what Nvidia application came installed on you PC. I have the option to simply right-click a program and choose to run it with the graphics card (also referred to as a GPU (dear, me...)). If your don't have this, you should at least have a Nvidia program where you can set specific applications to use it and not. The default setting is to not, and the fact you have no idea about this, makes it likely to be your problem.
The task manager idea really isn't the best idea, but in the task manager, highlight the process in the list, right-click, and there is an option to increase CPU activity. In all likelihood this is not gonna help anything, so I wouldn't really bother with it.
QuoteBut the topic is really about what to buy and replace.
Or I suppose the last option is just throw money at it an hope for the best. What I am trying to tell you is you don't have to. I have run games with PC's with less performance. If your dead-set on spending money and still not understanding your computer, simply buy a new one, with the highest upgrade available for every component that the manufacturer offers. This way you don't need to learn, and your games will run good.