Options are, Plug and play ecu, many benefits with these can fit them yourself, 5 mins research an you'll be clued up. Cost 500 + ish quid 2nd hand. Or go down the piggyback ECU route, EMB for example, someone needs to map it for you. Cost 550 at the cheapest and you will need it mapped again after every engine mod you do after the original map. Anyway both remove the speed limit, they do lots more than that though.