What's a good upgrade path for me?

[balanceballs]

I have this spec currently:

Intel i5 2500k @ about 4ghz, with Hyper 212 evo
Corsair TX750 power supply
ASUS P8Z68-V PRO motherboard
8GB G-Skill "Ripjaws X" RAM
Sapphire Nitro RX480 (8GB)
Various HDDs & a Samsung 840 SSD
Monitors, etc.

I'm finding it struggling quite a bit with some newer titles like Assassins Creed Origins and would like to upgrade a few bits to help it out! I reckon I should upgrade my CPU and get DDR4 RAM, is this a good idea and can I do it within budget?

Budget will be about £350 - what am I best spending this on?

Thanks

 

[balanceballs]

Thanks for the suggestions. RAM seems to be expensive?! I know it goes up and down but wow.

My monitors are both 1080p, not planning to upgrade any time soon.

I've read that my CPU could be a limiting factor, would a graphics card upgrade really see a huge benefit?