You can also retime any of your keyframes by revealing them in the timeline (press the u key), selecting the property or draging a marquis around the keyframes you want to change, and then hold down the Alt/Option key and click and drag the last selected keyframe to change the overall timing of the animation.
Many questions about keyframes can be answered by simply going to the After Effects Help files and clicking on the first link under After Effects help and tutorials then click on something like Editing, moving, and copying keyframes in the Animation and Keyframes section.
There you will find these instructions:
Expand or contract a group of keyframes in layer bar mode
- Select at least three keyframes.
- Hold down Alt (Windows) or Option (Mac OS) and drag the first or last selected keyframe to the desired time.