Adding inches to a shirred jsk?

Hello, everybody. I recently bought a BodyLine dress, and like a fool, I bought a size M like usual. This size M through, alas, is smaller than the average size M- with the sheering. I assume I need to add four inches but I am stuck on removing some pleats and redoing the shirred panel, adding cloth to the bodice.. All that. Will anyone be kind enough to post tips and links if possible?

**Mods, if you feel like this post is spam, Please feel free to delete it. All I ask is that you contact me so I can know what I did wrong and avoid doing it in the future. Thanks.