A stack has changed its height!

I have a total of seven stacks, stacked up in one column.
Somehow one of them has changed its height on its own!

Where can I go in to resize this stack to match the other
six?

Thanks!

I just figured it out! 

It's the obvious. I was able to just drag the border
up/down to adjust it.

I don't know why I didn't see it before!