Help-PC upgrades for sims gaming

Hi,

Needing some help/advice in updating parts for my computer for sims. 
I play with lots of mods and cc (50gb) worth. My computer runs okay atm but could be better so wanting to know if there are things I can upgrade for it rather then buying a whole  new PC .I have been told that my graphics card may not be getting utlised due to some parts but unsure as I have no idea when it comes to computers. 

But if there is nothing that can be upgraded and I need to buy a new PC, any suggestions? 

I have:

Intel(R) Core(TM) i5-4590 CPU @ 3.30GHz 3.30 GHz

24GB DDR3

Intel(R) HD Graphics 4600

Motherboard: Asus rock B85m pro 3 

If need more info on my computer let me know. 

Thanks