You have several locations where you can change your video’s name!
In the Workspace
You can change your video’s name while editing your project. Hover your mouse over the title in the upper left corner of the workspace, and click on it to open the edit field.
On the Share page
You’ll have the option to change the name of your video on the Share page too! Click on the name of the video and that will open the edit field so you can change the name.
On the My Projects page
You can change your video's title by clicking on the name on the My Projects page. Hover your mouse over the title, and click the pencil icon that appears. That will open the edit field. Write the new name, click enter, and you're set!