Click "export to storyboard" (the button just under "3. Tools"), go to "Frame" / "Frame size" / "Change size" and check "Proportionally resize image". You get a new animation of a smaller unit, you just need to "export to FLC" and that's it. Very easy, and the palette is kept so no worry. I tried it today for the first time and it's so easy that I really should've tried it earlier. Most of the time you don't notice the loss of frame and if you don't want to push things too far, it will do the job.