Welcome to the community. 
4GB of RAM, these days, is mostly considered to be on the low-end of PC gaming. And I feel your pain. I’m not an expert in building or modding PCs, but my suggestion would be to replace your RAM for something better (possibly 8GB minimum). Maybe @ptondo or @Chris can suggest/recommend something here.
Another thing I can suggest is lowering the game’s graphic settings so that it may use slightly less of your PCs resources.
Otherwise, there is a list of some awesome low-RAM games here, including some that may surprise you: A list of games for your low-spec potato computer.