looks for like i5-2500k/i5-3550k, Z77 board, 8gigs or something of DDR3 1600mhz or more and a GTX 670 build.
and last but not least 128gb SSD if u got money for that, i t hink that would be what would be a good upgrade if u wanna game ^^
maybe something like this?
http://www.scan.co.uk/products/29-4i...art-cache-34x-
http://www.scan.co.uk/products/asus-...dvi-i-hdmi-atx
http://www.scan.co.uk/products/8gb-%...9-9-24-xmp-15v
http://www.scan.co.uk/products/2gb-m...79mhz-cores-13
http://www.scan.co.uk/products/128gb...rite-320mb-s-2
i5-3550k/p8z77-v pro/8gb/gtx670 power edition oc/128gb ssd that's around €791 than there is also budget for case, psu or anything else u want or think u need.