Using the Track Editor, you can independently modify the animation's start or end point. This changes the animation's overall duration and scales the keyframes. Dragging the start or end point compresses or stretches the keyframes in the selected channels. If you want to simply move the first or last keyframe to another point in time, drag the keyframe.
To adjust an animated channel's start or end point:
The corresponding track in the Track Editor turns light blue and its keyframes appear.
To scale an animated channel's timing:
The corresponding track in the Track Editor turns light blue and its keyframes appear.
As you drag the handle, the keyframes in the track scale proportionally to the amount you move the handle.