Upgrading Old Parts.

HUGE PROPS TO ALL THAT HELP ME HERE I HAVE PRETTY MUCH NO IDEA ABOUT ANYTHING RELATED TO THIS TOPIC

I'm planning on replacing some parts in my old "Gaming PC" I made a mistake and bought a premade. An Alienware x51 r2, I plan on replacing the graphics card and getting more ram for it. My goal is to try to get Watch_Dogs 2 to run at 60 fps on low settings. It currently runs at 20 fps. I would like suggestions of what to buy and replace, as I'm not that tech-savvy, and I'm afraid I will make a vital mistake. I will list my current specs (that I believe I need to list, tell me if you need any more) bellow.

Microsoft Windows 10 Home ACPI x64-based PC Intel(R) Core(TM) i5-6400 CPU @ 2.7GHz, 2712 Mhz, 4 Core(s), 4 Logical Processor(s) Installed Physical Memory (RAM) 8.00 GB Total Physical Memory 7.91 GB Available Physical Memory 2.99 NVIDIA GeForce GTX 745 Intel(R) HD Graphics 530