There was a 4% chance that your choice (box #7) was right. You haven't changed your choice, and the people in boxes #7 and #8 haven't moved, so there is still only a 4% chance that your choice is right. Since the woman is either in box #7 or box #8, there must therefore be a 96% chance that she is in box #8. So you should definitely change to box #8!

Here is another way of looking at it. You chose box #7 at random. However, if you were wrong (which you almost certainly were), the gameshow host chose box #8 knowing that it was right. So box #8 is almost certainly right.