You can edit videos that you've uploaded or recorded into My Media inside Canvas in two ways:

1) You can edit the "meta-data" for the video, such as the title, descriptions and tags. This guide shows you how: How do I edit the title, description and other information about a video?

2) You can edit the video itself by trimming footage off the beginning or end, or out of the middle. This guide shows you how: How do I use the Kaltura Video Editor?