Hello Makai and welcome to the A2OC!
I see from your profile that you are the proud new owner of a 1.4 petrol. Unfortunately, the tuning options for this engine do not give good returns in terms of power for the costs involved - 5-10 bhp maximum is the best you can hope for, but the cost of a remap will be around £250 from a reputable specialist.
Don't even consider a plug in box, as most of them are nothing more than a cement resistor that fools the engine into thinking it's running lean, so increasing consumption.
At worst, they can burn the valve seats on the top end, ruining the engine. At best, you will see a very small power increase, but have a wallet £150-or so lighter!
Cheers,
Mike