For a time, Gregor is ashamed of his condition and tries to hide from everyone. In what way might this be called a step forward for him?

This is an interesting question which I imagine could engender a diverse discussion with many possible answers. One way we might approach this is by Gregor's forced self-examination. Before, when he was just another cog in a capitalist social machine, he was never able to face his existential situation. Now, though, the opportunity to self-reflect presents an attempt to be somewhat authentic in regards to his struggles with his identity.

He gets a chance to see how his life is like without working for his family anymore and tastes the life of being free. Before, he always had to get up early and face his co-worker and boss but now he gets to stay at home and relax.