How do I change the bounds of a symbol?

I have created a symbol, consisting of several animated elements. The symbol has it's own timeline, and is part of a larger composition.

Now that I have created the symbol, it turns out that I need to change the size and position of some of it's elements, so that they now extend beyond the original boundaries of the symbol. The problem is that on playback, the symbol seems to clip to it's original boundaries, and I don't know how to adjust those to fit the new layout.