Be careful adding new RAM. Do you know the exact model of your old RAM? If the Corsair you linked and the RAM you own have different specs, you could run into some problems.
As for your fps issue, why do you think you need more RAM? When you're playing Tera and you check RAM usage with Task manager, is your usage rally high? I'm not sure why you're getting such poor FPS for that game. I just looked up the system requirements and yours blow then away.
Just check to see if having too little RAM is actually the problem.