What should I upgrade First? Config system

[Clovis48]

Hello

I am looking to upgrade my PC that starts to run some games with difficulty.
Which part should I upgrade to get the most significant improvements? I am looking at a list of priority really if that is possible. I can spend around 600euros at this stage on components parts.

My config:

Processor: i5-4590 CPU @3.30 GHz, 4 Cores
Graphics Card: GeForce GTX 770
MotherBoard: ASRock Z97X Killer, Intel LGA 1150
Memory: 8GB DDR3 799.6 Mhz
Power Supply: 650W

I play for the moment in 1920 * 1080 but may upgrade my screen later this year as well.

Thanks for your answers

Clovis

 

[CountMike]

GPU is first that comes to mind.