Hi there!

Be sure to point your cursor ovetop the video, then a red control bar should appear along the bottom of the video. On the right hand side, there are 3 icons - volume, settings, and full screen. Click the settings icon (which looks like a cog from a wheel) and a sub menu should pop up that says SPEED and gives you choices like x.5 x1.5 x2.5 etc.

Let me know how it goes!
Mikew