Jengallan :
Well i was looking at the AMD FX8320 8 core and the ASUS AMD AM3+ 760G 2*DDR3 8*USB2.0 GBE LAN Micro-ATX MOTHERBOARD as a reasonable upgrade, just as long as its a good upgrade for my money and wont break everything, also i have no sound card and use the nvidia gt640 just to give you some specs
For about £300 you can get quite a good upgrade:
PCPartPicker part list:
https://uk.pcpartpicker.com/list/DvXvd6
Price breakdown by merchant: https://uk.pcpartpicker.com/list/DvXvd6/by_merchant/
CPU: Intel Core i5-4590 3.3GHz Quad-Core Processor (£189.99 @ Amazon UK)
Motherboard: Asus H81M-PLUS Micro ATX LGA1150 Motherboard (£49.99 @ Amazon UK)
Total: £239.98
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-11-29 14:09 GMT+0000
There's also this for a bit extra:
PCPartPicker part list:
https://uk.pcpartpicker.com/list/TKzZgs
Price breakdown by merchant: https://uk.pcpartpicker.com/list/TKzZgs/by_merchant/
CPU: Intel Core i5-6400 2.7GHz Quad-Core Processor (£170.99 @ Novatech)
Motherboard: MSI H110M Gaming Micro ATX LGA1151 Motherboard (£59.99 @ CCL Computers)
Memory: Corsair Vengeance LPX 8GB (1 x 8GB) DDR4-2400 Memory (£49.64 @ Ebuyer)
Total: £280.62
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-11-29 14:10 GMT+0000
This allows a greater upgrade path, with it being the LGA1151 Socket, you can upgrade to an i5-6500, 6600, or 6700, if you wish to overclock you'd have to change motherboard again, but this allows a good upgrade path in the future.
With the first build, you can re-use the RAM in your current build.
Edit: You can also drop the i5-6400 to an i3-6100, and that gives you some extra money, so if you save up a bit extra you can purchase a GTX 1050 or GTX 1050Ti to upgrade your GPU.