Not too difficult. If you open the file in Paint, you can select the region, and there should be a function allowing you to flip along the x-axis or y-axis. You should try flipping along the x-axis, or in other words, flip vertically. After that, you may need to open it in a skin edittor, like Skin Edit, because Paint will save the file without transparency, making the Hat region empty until editted. Strange glitch, but easily fixed.
Hope this helps!