About £500 For a gaming PC, what should i change?

Solution
with that small budget, I will run win 10 as trial and buy later on. Win 10: https://www.microsoft.com/en-us/software-download/windows10 Download tool and make a boot-able usb. Dual core is not enough any more, quad is kind of a must nowadays.
My edits:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Core i3-8100 3.6GHz Quad-Core Processor (£89.94 @ Aria PC)
Motherboard: ASRock - B360M Pro4 Micro ATX LGA1151 Motherboard (£64.99 @ Overclockers.co.uk)
Memory: Patriot - Signature Line 8GB (2 x 4GB) DDR4-2400 Memory (£77.94 @ Amazon UK)
Storage: Seagate - Constellation ES 1TB 3.5" 7200RPM Internal Hard Drive (£24.59 @ Aria PC)
Video...
with that small budget, I will run win 10 as trial and buy later on. Win 10: https://www.microsoft.com/en-us/software-download/windows10 Download tool and make a boot-able usb. Dual core is not enough any more, quad is kind of a must nowadays.
My edits:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Core i3-8100 3.6GHz Quad-Core Processor (£89.94 @ Aria PC)
Motherboard: ASRock - B360M Pro4 Micro ATX LGA1151 Motherboard (£64.99 @ Overclockers.co.uk)
Memory: Patriot - Signature Line 8GB (2 x 4GB) DDR4-2400 Memory (£77.94 @ Amazon UK)
Storage: Seagate - Constellation ES 1TB 3.5" 7200RPM Internal Hard Drive (£24.59 @ Aria PC)
Video Card: Palit - GeForce GTX 1050 Ti 4GB StormX Video Card (£148.79 @ Aria PC)
Case: Thermaltake - Versa H21 ATX Mid Tower Case (£30.51 @ Amazon UK)
Total: £436.76
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-06-05 19:23 BST+0100

46 pounds psu: https://www.amazon.co.uk/Corsair-CP-9020120-UK-CX450-Bronze-Supply/dp/B06WW51XBX
 
Solution
Optimized with better parts...

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Core i3-8100 3.6GHz Quad-Core Processor (£89.94 @ Aria PC)
Motherboard: ASRock - B360M Pro4 Micro ATX LGA1151 Motherboard (£64.99 @ Overclockers.co.uk)
Memory: Patriot - Viper Elite 8GB (2 x 4GB) DDR4-2800 Memory (£81.48 @ Amazon UK)
Storage: Seagate - Barracuda 2TB 3.5" 7200RPM Internal Hard Drive (£50.39 @ Aria PC)
Video Card: Asus - GeForce GTX 1050 Ti 4GB Phoenix Video Card (£149.99 @ Aria PC)
Case: Thermaltake - Versa H21 ATX Mid Tower Case (£30.51 @ Amazon UK)
Power Supply: Corsair - CXM (2015) 450W 80+ Bronze Certified Semi-Modular ATX Power Supply (£49.99 @ Corsair UK)
Total: £517.29
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-06-05 19:27 BST+0100

You can activate Windows down the line. Should not affect performance... https://www.howtogeek.com/244678/you-dont-need-a-product-key-to-install-and-use-windows-10/
 

shmoochie

Commendable
May 10, 2018
900
4
1,715
I think that is an excellent build for the price. You could add a small ssd for faster bootup but it's not necessary. I think Kingston sells a 120Gb for like ~$30. My only problem with the build as a whole is that it is not very future-proof. It'll definitely play those shooters now, but it might have trouble playing games in a couple of years and an upgrade will involve buying a new mobo and processor.
 


And that is why a dual core build is not viable in 2018. A quad core build like 8100 should give more longevity as well as performance in most games, if not all.