pc building

I just want to uprade my pc's ram from 2gb to 6gb(2gb+4gb).....when i went to nearest pc shop,they said that i need to get 64bit to use 6gb ram....I said ok just do it....they later told me that i need to format my pc in order to get 64bit system because there is not enough space(it has 50gb) in...

I'm ordering a custom built PC, but Im not an expert when it comes to components and PC building in general. This are the specifications on the PC that I want to order, and I wonder if it will be able to run new and upcoming games, like Call of Duty Modern Warfare or Cyberpunk 2077 for instance...