In this tutorial (https://pytorch.org/tutorials/beginner/blitz/neural_networks_tutorial.html 7), it says that:

Note: Expected input size to this net(LeNet) is 32x32. To use this net on MNIST dataset, please resize the images from the dataset to 32x32.

I dont understand where in the network we define it that the input should be 32x32.
I also try different input and it gives me error but im not sure why?
What should i do if i want to change the size from 32 to 120x120 for example?