Save:
checkpoint = {'model': Classifier(),
          'state_dict': model.state_dict(),
          'optimizer' : optimizer.state_dict()}

torch.save(checkpoint, 'checkpoint.pth')

Load:
def load_checkpoint(filepath):
    checkpoint = torch.load(filepath)
    model = checkpoint['model']
    model.load_state_dict(checkpoint['state_dict'])
    for parameter in model.parameters():
        parameter.requires_grad = False

    model.eval()
    return model

model = load_checkpoint('checkpoint.pth')