Can anyone improve my build but stay within £500

Solution
No sense buying older Haswell parts when brand new Skylake is in your price range-

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-6500 3.2GHz Quad-Core Processor (£169.99 @ Amazon UK)
Motherboard: Asus H110M-A Micro ATX LGA1151 Motherboard (£49.99 @ Novatech)
Memory: Kingston HyperX Fury Black 8GB (1 x 8GB) DDR4-2133 Memory (£27.25 @ Amazon UK)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£37.98 @ Novatech)
Video Card: Asus GeForce GTX 960 2GB Video Card (£149.99 @ Novatech)
Case: BitFenix Nova ATX Mid Tower Case (£26.99 @ Overclockers.co.uk)
Power Supply: SeaSonic...
Yup. Changed the RAM & GPU. Graphic card changed to GTX 960. More horsepower & much faster.

The RAM is changed to a dual channel memory kit to be more compatible with each other. But also for its higher frequency. Your mobo may default the RAM speed to a lower one. But that can be increase by overclocking the memory which this memory supports.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor (£145.36 @ More Computers)
Motherboard: Asus H81M-PLUS Micro ATX LGA1150 Motherboard (£42.95 @ Amazon UK)
Memory: Corsair Vengeance Pro 8GB (2 x 4GB) DDR3-2400 Memory (£32.99 @ Amazon UK)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£37.98 @ Novatech)
Video Card: EVGA GeForce GTX 960 2GB SuperSC ACX 2.0+ Video Card (£159.96 @ Amazon UK)
Case: Corsair 100R ATX Mid Tower Case (£42.98 @ Amazon UK)
Power Supply: EVGA 430W 80+ Certified ATX Power Supply (£32.99 @ Novatech)
Total: £495.21
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-05-02 13:07 BST+0100
 
No sense buying older Haswell parts when brand new Skylake is in your price range-

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-6500 3.2GHz Quad-Core Processor (£169.99 @ Amazon UK)
Motherboard: Asus H110M-A Micro ATX LGA1151 Motherboard (£49.99 @ Novatech)
Memory: Kingston HyperX Fury Black 8GB (1 x 8GB) DDR4-2133 Memory (£27.25 @ Amazon UK)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£37.98 @ Novatech)
Video Card: Asus GeForce GTX 960 2GB Video Card (£149.99 @ Novatech)
Case: BitFenix Nova ATX Mid Tower Case (£26.99 @ Overclockers.co.uk)
Power Supply: SeaSonic ECO 430W 80+ Bronze Certified ATX Power Supply (£38.36 @ Ebuyer)
Total: £500.55
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-05-02 13:22 BST+0100
 
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