Upgrading amps of a circuit to 12A

Hi,
I did motorize my kid's electric car with a 12v wiper motor that burns out any fuse lower than 12A because of it's high current at start. I think it's running amperage is about 6A.

I found this great circuit that fits almost exactly in what I want, except that it have a bit weak output amperage.
here is the circuit:
http://www.soloelectronica.net/dcdc_12v_a_18v.htm

I think this is also great because of the potentiometer for the output current that will be very useful.
If anyone with such knowledge in electronics could help me to replace a few components that help rising the output power would be perfect!!!
I also know that for this high current I should enlarge the pcb traces and place loads of solder on it.

best regards!