Pepakura and changing proportions

Greetings,



I'm quite new to pepakura and I wanted to make an Ironman suit for my 3yo son. Lucky for me, there are plenty of Iron Man .pdo files around the net. My problem is that his proportions are not those of an adult. I tried to change the proportions of the models using pepakura with no luck. I also tried using Sketchup but I had no luck either. So I wanted to ask what is the best way to change the proportions of an already existing .pdo file? Thanks in advance!