I think this advice - given by Bob Proffitt in https://www.cnet.com/forums/discussions/pc-upgrade-reccomendation/ is quite good.
I assume you checked your motherboard (you didn't tell make and model) supports this latest generation CPU, possibly with a BIOS update necessary. Check the CPU compatibility list on the makers site before buying it.
Firstly, sorry for the amount of posts, I just want to ensure the best upgrade for my PC.
For the future the main games I will be playing are COD WW2, Fifa 18 (when they are out), Rocket League, GTA and CSGO. I play these games at 4k and I'm unsure whether to upgrade my CPU (mobo and ram) or a GPU.
I would be planning to get an i5 7600k and mobo and ram or a GTX 1070.
My current PC, i5 4460 and GTX 970.
In some games I see lag, fps drops and freezing.
What would be the best upgrade?