In Flash CS5, after you've inserted a keyframe in a motion tween, how do you move that keyframe to another frame?
Make use of MotionEditor. Select Window >> Motion Editor. from main menu.
Details on Motion Editor here: http://help.adobe.com/en_US/flash/cs/using/WS0B461DB7-C633-4c1a-9855-44483601E912.html
You do not need to use the motion editor if you don't want to, you can do this in the timeline. Ctrl+click the frame on the motion tween span, and then drag it to a new location.
Thanks guys - both helpful answers.
The motion editor is great for fine tuning the tweening, whereas the second method is ideal for quick idea changes.