It's actually pretty easy. Just jack up the cover and slide a more
powerful welder underneath. To not be so flip, the transformer in the
machine limits current output, so you would need to replace the
transformer to get more amperage out of it. And then maybe replace a
current sensor or heat sensor that shuts down the machine when it gets
too hot. And then maybe replace the cable and gun because the ones you
have now are designed for a lower amperage than you want. And the
rectifier might need to be upgraded also. You would be better off
selling it and buying a bigger machine. How much current do you need?
You might be limited by the power available. If you anly have a 120
volt circuit to plug into that limits your options to low current
machines. Do you have a torch? You can weld heavier sections by
pre-heating the metal. Harbot Freight sells a weed burner that works
great for heating up large pieces of steel or aluminum.