XF 1.5 How do I upgrade a style without losing any changes?

So I've upgraded my xenforo to 1.5, but the problem is I'm not really sure how to upgrade the style to 1.5 without losing any changes I've made to it. Normally, you'd have a child style that has all the changes to it so you can simply overwrite the parent style, keeping all the changes because of the child style. But the problem is, at the time of installing the style I never made a child style that contains all the changes, so is there still a way to upgrade the style, without losing any changes?