Resizing the current shadowbox frame

So, I have a site right now where we have a smaller post that pops up in a shadowbox. Those posts contain images, and I’d like to use the same shadowbox window to display the full image when the person checks on them. Right now, it creates a shadowbox within a shadowbox, which isn’t really necessary.

How could I go about doing this? Is it built-in, or will it take some hacking?

Best,

Andrew