Navigate to the URL of the clip you'd like to delete and click Settings, then Moderation. You can also delete clips from your Clips page. Please see Managing Clips for more information.
To delete multiple clips at a time, click the checkbox next to each clip and then click Delete Selected, which should have appeared at the top of the table. To delete all the clips of your channel, click the 3 Vertical Dots menu icon above the top right corner of the table, and you will see the option to Delete All Clips of My Channel.