Hold CTRL, click/hold the left side of the event, and drag.
You can also right click, go to Properties, and set the speed there. .500 for instance, is half speed.
- Put the mouse pointer on the left or right edge of the clip until the pointer turns into a left-right arrow (it also shows a small rectangle on the side toward the clip)
- Hold down the Ctrl key and watch an uneven underline appear in the pointer
- Hold down the left mouse button and slide the clip toward the center of the clip to speed it up, away from the center of the clip to slow it down.
You can speed up or slow down a clip to a factor of 4. If you need more drastic changes you need to render the clip, put the rendered output back in the timeline and then you can change it again up to a 4x factor.