To turn up the volume of a video, open the lesson page to view the video. Hover your mouse over the video to pull up the video player menu on the bottom of the player.
Hover your mouse over the speaker icon to open the volume slider. Click on the white dot and move your mouse to slide your volume to the correct level. Sliding the volume up increases the volume, while sliding the volume down decreases the volume.
To mute the video, you can click on the speaker icon. To unmute the video, you can click the speaker icon again.