> My question is should I replace the motor wires to heaver wire
The motor wires are simply a continuation of the solid strand wires of the motors themselves. They are covered with black, yellow and red heatshrink to identify the windings. It would serve no purpose to replace the wiring from the ESC board to the motor. More damage has been caused by the hot MOSFET chips melting the wires. Therefore, while you're in there, route the motor wires so they are not in direct contact with the six MOSFET chips. Nothing else on the ESC produces any significant heat.
As previously mentioned, take note of the wire colors. They are black, yellow, red on two ESCs and black, red, yellow on the other two. I would replace the ESCs and motors one at a time to ensure you get it right.
I replaced my ESCs with ver. 2.1 this weekend, and so far a couple of happy flights.
Paul