[Help] Upgrading my PC

I have a custom build desktop pc, which is over 3 years old now.
I thought of uprading it, so I'll be able to play new games in the next 3 years on high specs again.

Are there any suggestions on what I should buy? (probably a 4GB graphic card?)
Here are my specs:

Thanks in advance

I'm not quite sure if it's worth 200€ to upgrade from 3.3 to 3.4Ghz, if I'd change my cpu, I'd probably pay 100€ more for 4Ghz.
But do I really need this to run a good (4GB) graphics card? I thought of getting the AMD Radeon R9 290X, when it's max. 350€.

PS: Noob question, ik. I just don't know much about this stuff and don't want to buy something wrong.

Zitat von Sea Shepherd

When it comes running a 4gb gpu you're completely fine with the i5 2500k, but you need a powerfull enough power supply. You didn't list the power supply in you specs, can you find out wich one you have, atleast how much watt ? (your cpu is fine, i would rather overclock it than buying another one)

Is 550W (Cooler Master V550S) enough? I've just seen a special offer for this.