How can I modify the Y-axis of an existing plot in a .fig file?

I have spent a fair amount of time constructing a .fig file, and I need to make one change, but I'm not sure how to do it.

I plotted on my Y axis in terms of volts, but I want to change it to millivolts.

I can easily change the ylabel, but I'm unsure how to multiply the numbers in the plot by 1000.

Any ideas?

Thanks,

Mark