Computer Build: Will this work?

I am trying to add some things onto my desktop. Things I'm trying to add; Graphics card: GTX 7950 3gb Ram +4 (already has 4gb) Processor: AMD FX4130 X4 Quad Core 3.8GHz Black Edition AM3 What my computer has currently: processor: Intel quad cpu 2.33 GHz Graphics card :Nvidea GForce 8400 GS 4 gb ram Question is; This is my first time building a computer. Can I just take out the graphics cad, processor etc, replace them? Or is there more I need to worry bout like compatibility things. also does it need to be the same type of ram ? Thanks :)