Upgrade or a complete new PC?

Wuzzsup

I already asked in some forums for a good advice but I only got shit...
So I would like to play CoD:AW (or in general new games) without laggs. It does not need to be on high res , Im fine with low res already, that means it should be about 70-90 fps...
1st of all my pc specs :
Processor : Intel Core i3 CPU 540, 3.07GHz
Video Card : AMD Radeon R9 200 Series (270x , I would like to keep that one tho)
Memory : 8 GB
Operating System : Microsoft Windows 7 Home Premium Edition Service Pack 1 (build 7601), 64-bit
Tell me if i should add something.

So since I lagg like shit in CoD:AW I just would like to upgrade my pc , could you tell me what I should buy?
Some guys already said that I need to buy a new "base/socket" (dont know the real english translation) but I recently bought that video card so I dont really wanna buy a new one and yeah like I said... I dont really know what to buy x)

ty for help