Will upgrading a cpu improve performance or fps? (For gaming use)?

Will upgrading my cpu improve my performance or fps? What I have…

Asus a55m-s motherboard
500w power supply
Nvidia geforce 660
AMD a6 5400

If it helps… I mostly play Black ops 3, Dark souls 2, Minecraft, Mortal kombat x, Eveonline, Team fortress 2, Games like that.

Jiovanni 17.02.2016

While upgrading your CPU will improve SOME performance, upgrading your GPU (swapping out your GeForce 660 for GeForce GTX 960) will likely give you the most performance gain… Assuming your system can support it.

TStodden 18.02.2016